CHAPTER 4. HOT Lane Operations and Management
Vehicle movements between highway mainline lanes and HOT lanes must be managed carefully, with well-designed ingress and egress to avoid unnecessary bottlenecking, violation and unsafe weaving. Special attention to enforcement techniques, particularly with respect to verification of vehicle occupancy, is necessary to regulate demand and maintain facility integrity.
Effective lane or facility geometry is a critical prerequisite to achieving LOS design and safety goals. Another important function is the ability to capture and identify user data for automatic billing. This requires an integrated system of in-lane devices with back office support that not only provides account management, customer service support and violations processing but also ITS support functions such as 511, advanced traveler information and incident management. The purpose of this chapter is to describe the basic element of effective HOT lane operations and management.
When converting to a HOT lane within a larger highway network, consideration must be given to weighing appropriate balance between eligibility, level of service and pricing conditions in order to achieve effective and sustainable lane management. Determining peak hour volumes in highway mainline lanes and HOT lanes and establishing the minimum desired LOS in the HOT lane is the initial step in establishing a lane management process. The lane management system must establish LOS performance objectives and determine the maximum allowable peak hour volumes to achieve those objectives. The HOT lane pricing conditions function as a tool to manage traffic flow against the LOS performance objectives.
Without effective lane use management, there is a risk that the commodity being sold to the public – i.e. time savings over highway mainline lanes – will be greatly compromised. HOT lane traffic levels should be limited to volumes that provide reliable speed advantages over adjacent highway general purpose lanes. There are two critical issues that affect lane management:
HOT lane capacity is a function of the number of access points, the vehicle mix, roadway slope and configuration, separation treatments, and the number of travel lanes, among other variables. HOT lanes with fewer access points have higher lane capacity with those with more access points. Likewise, a multilane HOT facility will have a higher managed capacity (vehicles per lane per hour) than a single HOT lane configuration. For example, flows on the Houston I-10 Katy Freeway QuickRide – a one lane, reversible-flow facility are kept to 1,500 vehicles per lane per hour. In contrast, the 91 Express Lanes – which provide two travel lanes in each direction – operate at acceptable conditions with flow rates of 1,800 vehicles lane per hour.
On an unpriced highway, increasing volumes result in decreased speed. When the volumes reach an unstable point, speeds to drop to around 15-20 miles per hour. With this reduction in speed, lane capacity will drop from 2,000 to 2,100 vehicles per lane per hour to about 1,300 vehicles per lane per hour. In order to maintain “free flow” conditions in HOT lane facility, vehicle throughput is regulated through variable pricing to a level below maximum capacity. This volume threshold serves as the benchmark for ensuring premium level of service for HOT lane users.
In summary, lane management strategies to regulate traffic flow on HOT lanes include:
The impact of each lane management tool is briefly presented in the adjacent table. Applied in combination, these tools offer the flexibility needed to maintain strong LOS on the HOT lanes. An appropriate range for HOT lane capacity in most project settings would be approximately 1,600 to 1,800 hourly automobile equivalents per lane.
Toll collection systems may consist of conventional cash lanes, dedicated electronic toll collection lanes or Open Road Tolling (ORT). If at all possible, toll collection must have a seamless customer interface and, equally importantly, have no negative impact on traffic flow. ETC is used on nearly every significant toll road, bridge, and tunnel in the country. These technologies are well-proven and provide the type of seamless customer interface and transaction reliability that make them critical to HOT lane operations. The technologies used for electronic toll collection and pursuit of toll violators consist of Automated Vehicle Identification and Transponder Technology, Automated Vehicle Classification Video Image Capture and Account Processing and Customer Service. The electronic toll collection technologies for capturing tolls automatically is generally referred to as ETC (with a transponder) and Video Tolling (no transponder).
Most current AVI systems rely on Radio Frequency Identification (RFID) technology, which enables communication with a transponder affixed to a vehicle via Dedicated Short Range Communications (DSRC). A transponder is an RFID device that, when mounted on a vehicle’s windshield, enables the electronic collection of highway tolls by an AVI system as it passes through the toll zone. The ‘reading’ of the transponder may occur while the vehicle is traveling at stop and go or highway speeds. The AVI system typically consists of an antenna and reader installed above a toll lane to automatically “read” or identify the transponder, and the vehicle associated with it.
ORT and HOT lane implementation requires that tolling occur at highway speeds up to 100 mph. The difference between an HOT and an ORT implementation is the toll zone for an HOT implementation is lane based, generally one or two lanes, while in an ORT implementation a toll zone consists of multiple lanes. With both ORT and HOT implementations, there are no physical toll plazas, but the factors that determine gantry locations and how tolls are assessed are no different than those which determine conventional toll plaza locations. The features observed by the driver are the toll gantry (basically a highway sign structure) with the electronic toll collection equipment on it, the related support infrastructure, and toll signage to tell drivers that they are passing a payment point and how much is being charged. The technologies used in both implementations are basically the same.
Users who have established an automatic toll account are provided a transponder to install in their vehicle. The data written to the transponder at the time an account is established typically include information on vehicle classification, special group discounts, or special authorizations for a given vehicle type. When passing through a toll zone, the transponder data is compared with the in-lane monitoring systems to validate vehicle classification, special discounts or special authorizations that transponder and vehicle combination for a given account. Once proper account authorization has been verified, the applicable toll is then charged to the account and automatically deducted from a pre-paid account balance.
If the information on the tag and vehicle data do not correspond with a valid account, or if for some reason there is insufficient funds available in an account, or if the vehicle does not have a transponder, or has an improperly mounted transponder, the vehicle will be treated as a violator.
For many HOT lanes, SOV users are required to have a transponder while HOVs are exempted. Recent studies, however, have shown that requiring transponders on all vehicles improves enforcement through the use of visual indicators and/or video image capture of license plates. Requiring transponders in all vehicles, HOV, SOV, and transit, provides for easier identification of SOV and HOV vehicles or violators without a transponder, and for quick and easy implementation of special discount program rates at the back office and not in the lane.
Video tolling generally makes use of the open road toll enforcement cameras and the computer systems that support image and license capture, character recognition, and user location or citation processing. Video tolling allows the occasional user, tourist, or rental car motorist to establish a valid toll account either prior to using an ORT lane, or within a specified time after completing their trip. The time after trip completion is typically on the order of up to 72 hours. Generally a video toll account may be established by phone or WEB based interface with the motorist providing a credit or debit card number, vehicle license plate, make, model and type of vehicle.
Video toll accounts, using valid vehicle license plate numbers, are downloaded to the toll zone or lane controller and the video controller in the lane in accordance with procedures established by the facility’s Business Rules. If the motorist does not have either a valid transponder or valid video account the captured image is retained to be processes as a violation transaction.
The violation will be subjected to an image review process to determine if the license plate belongs to either a transponder customer or video toll account. If verified to be a valid license plate account the ‘violation image’ is converted to a toll transaction using the video image review and posted to the customer account.
The implementation of video toll systems in the lane use one or two video cameras with supplemental lighting to capture either the rear of the vehicle centered on the license plate area or two cameras to capture an image of both the rear and front of the vehicle. In facilities that restrict vehicle traffic to cars or two axle vehicles a single camera is sufficient to capture the rear of the vehicle and satisfactorily obtain an unobstructed and readable license plate image. For facilities that permit towed vehicles or semi-trailers, it is recommended that both front and read image capture cameras be used to ensure an unobstructed capture the truck’s front license plate and possibly the license plate of the towed trailer. It is essential that a front image capture be utilized for facilities with high truck and/or semi-trailer traffic since the rear license plate of the truck will normally be blocked by the towed trailer.
Image capture systems with camera and supplemental lighting may be mounted either overhead or along the side of the toll lane(s). The majority of image capture implementations use pulsed or flashed, high intensity LED white lighting since it is best suited to handling multiple colored license plate characters and backgrounds, and infrared lighting for license plate character capture in a black and white image. However, there are some implementations that measure ambient lighting and supplement with continuous lighting as needed to successfully perform optical character recognition on the captured image.
The millisecond flashes for pulsed and strobe lighting that are only triggered when an apparent violation (includes Vtolls) has occurred, or is detected must be unnoticeable by the user. Cameras mounted overhead with continuous white lighting is likely to cause visual impairment to the driver and should not be deployed for front license plates capture. Flashed/pulsed, strobe and infrared lighting solutions should be considered to avoid impairing the driver’s vision.
In order to ensure reliable system operations, the HOT lane facility must include operational resources to provide maintenance, customer service, and account management.
Enforcement is critical to the successful operation of any HOT lane facility. An effective HOT lane enforcement program should ensure that operating requirements, including enforcement of toll-exemption eligibility based on vehicle occupancy, are maintained to preserve travel time savings, discourage unauthorized vehicles, and maintain a safe operating environment.
This section reviews HOT lane operational concepts and identifies unique issues and challenges associated with HOT lane enforcement. Enforcement strategies used in several HOT lanes similar in scale and length to the projects reviewed in this study are discussed.
HOT lanes are toll facilities that charge a toll to all HOT lane users except for vehicles that meet the minimum occupancy for toll-exemption eligibility. In order to deter violations and reserve capacity for users, the HOT lane operator must be able to identify violators who use the HOT lane without paying. In addition, the HOT lane operator must be able to distinguish between vehicles required to pay the toll and HOVs that are eligible for toll-exemption.
Most HOT lanes today that utilize electronic toll collection require users to establish a pre-paid account from which toll transactions are debited for HOT trips taken. The requirement for users to have an active HOT lane account provides a partial solution for toll lane enforcement. Because all vehicles are required to have an active HOT lane account, motorists entering the HOT lane without a valid account are, by definition, considered in violation of the usage policy. Image capture technology is very reliable and can be utilized to read and capture license plate information. With this information, HOT lane operators can issue violation citations, collect tolls owed, and process fees.
The technology used for violation enforcement is similar to Video Tolling for image capture and license plate reading. All images of the license plates of suspected violators are sent to the VPC, the interface to the CSC for toll violation processing. The CSC contains infrastructure equipment, software and services to process violations and license plate read images. Once the VPC has confirmed that the captured license plate is not linked with a valid transponder, the VPC will link to associated VPC and/or DMV databases to obtain the identity and address of the vehicle’s registered owner, prepare billing for notification to the violator, and, if required, pursue that individual for reimbursement of tolls, fees, and penalties.
The enforcement system must be able to recognize HOVs that meet the minimum occupancy requirement and exempt them from the toll. In addition, the system must be able to distinguish toll-exempt HOVs from violators. Can this be accomplished without requiring all vehicles to establish a pre-paid account, including vehicles that will use the HOT lane primarily as toll-exempt HOVs? Based on the experience of recent HOT lane projects, the answer is no. Given the current state of technology, it is not possible to distinguish a violator from an eligible HOV from among the population of non-transponder equipped vehicles. Consequently, most HOT lane operators have chosen to require all vehicles, including toll-exempt HOVs, to establish active accounts with the HOT lane.
For HOT lanes that offer toll-exemption for eligible HOVs, the task of enforcement remains a major operational challenge. Why? Because there is currently no technology available that allows a HOT lane operator to assess a differential toll or provide a toll exemption based on observed vehicle occupancy. As a result, determination of vehicle occupancy has to be performed manually through visual inspection either at a fixed post or in transit. Another important wrinkle – given the operator’s inability to determine vehicle occupancy prior to a vehicle entering the HOT lane – is that the burden of realizing the HOV toll exemption is on the driver, not the HOT lane operator. In other words, the driver of the toll-exempt HOV must de-activate the transponder to prevent the HOT lane operator from inappropriately charging the toll. This in turn requires the enforcement system to be able to verify occupancy for HOVs that might otherwise be confused for a violator.
Facility design is also an important element of HOT lane enforcement. Barrier separation features can be effective in deterring potential violators, but barrier separated systems also require additional space along the facility to monitor, apprehend, and cite violators. Barrier separated facilities generally make apprehension fairly easy, since the violator is confined within the lanes after entry; however, it should be noted that the larger the facility (i.e., number of lanes) and the larger the quantity of entry and exit points, the more difficult manual enforcement becomes.
Non-barrier separated HOT lanes are more difficult to enforce, since it is easy to enter and exit the lane simply by changing lanes. Lane delineators such as those in use on the 91 Express Lanes in California can deter violators, with some instances of violators ‘diving’ through the delineators. Locations where delineators are used typically do not have adequate shoulder space for effective road side enforcement.
Some actions that can be taken to enhance the performance for HOV violation enforcement may include:
Enforcement is critical if a HOT lane facility is to be successful and effective. The enforcement strategy and the technology implemented must be reliable, highly visible, and one that promotes fairness. Most facilities currently use visual (manual) enforcement together with some technical support to monitor HOT lanes. Although utilizing enforcement vehicles to stop apparent violators may not be the most efficient method to catching violators, it is the most visible to the public, including the public traveling in the general purpose lanes. This visible enforcement effort demonstrates that the agency or entity controlling the use of the managed lanes is serious about maintaining the integrity of use by vehicles qualified to be in the designated managed lanes.
Enforcement of HOT lane usage must accomplish the following key operational functions:
Verify Toll Payment
Most current AVI systems rely on RFID technology, which enables communication with a transponder affixed to a vehicle via Dedicated Short Range Communications. A transponder is an RFID device that, when mounted on a vehicle’s windshield, enables the HOT lane operator to collect an electronic toll as it passes underneath the toll zone.
The ‘reading’ of the transponder may occur while the vehicle is traveling at stop and go or highway speeds. The AVI system typically consists of an antenna and reader installed above a toll lane to automatically “read” or identify the transponder, and the vehicle associated with it.
Verify Vehicle Occupancy
As stated earlier, accurately determining the number of vehicle occupants poses a tremendous challenge. When volumes rise, it is difficult to catch all violators, let alone distinguish violators from eligible HOVs. From time to time, an enforcement officer mistakenly stops HOVs because an occupant in addition to the driver (e.g. small child) is not readily visible in the back seat. Enforcement of occupancy requirements is perhaps the most difficult operational challenge facing toll agencies; this is because automated technologies have not yet met reliability and field accuracy requirements needed for operational deployment. In addition, there are a host of cost and privacy considerations associated with the use of such detection technology.
The technical support used to supplement manual enforcement typically consists of a gantry-mounted violation indicator light to provide an indicator for near-by enforcement vehicles to act on. Additionally, some facilities use video cameras together with an OCR system to capture the license plate image of the vehicle as it passes through the toll zone. The camera may be mounted above the roadway or along side the roadway, depending on the geometry of the HOT facility and the violation objectives of the facility. Once the license plate image is captured, it must be correctly ‘read’ by the OCR in order to successfully locate the vehicle owner to collect the toll and if applicable, the toll evasion fine.
Assess Fine to Violators
Violations fall within two classes: a) enforceable (no transponder read, but license plate read; vehicle not linked to an active account), and b) Unenforceable (no transponder read and no license plate read). An effective HOT enforcement program should attempt to keep violations (enforceable and unenforceable) to at or below 10 percent of total trips.
HOT lanes typically require the creation of local ordinances that carefully document the process for resolving violations. The ordinance should establish a multi-stage notification process, in addition to establishing fine notification procedures that are consistent with the Georgia vehicle code. A multi-stage notification process with a graduated fine structure is typically used to provide differential penalties for first-time violators versus habitual offenders.
In California, for example, the 91 Express Lanes uses the following graduated violation structure:
The Orange County Transportation Authority (OCTA) reports that of the total number of enforceable violations, 60 percent are dismissed with no penalty, 11 percent pay toll + penalty and 20 percent go to collections. In total, 80 percent of all enforceable violations are addressed at the NTEV/NDTEV stage.
I-15 Express Lanes (San Diego, CA)
The I-15 Express Lanes is a barrier-separated, reversible flow HOT lane that has recently expanded from an 8-mile facility (with two toll zones) to a 20-mile facility with multiple access points. Because of the limited roadway geometry and restricted shoulders, shoulder enforcement on the extended segment is a major challenge. The mode of enforcement will require more mobile enforcement capabilities, with use of supporting reader technologies in mobile units.
The San Diego Association of Governments (SANDAG) contracts with the California Highway Patrol (CHP) to perform manual enforcement at designated enforcement areas. Under this contract, CHP periodically supplements the fixed post visual enforcement with mobile enforcement units. SANDAG reports enforcement remains one of the biggest challenges facing the day-to-day operations of the I-15 Express Lanes, especially given the opportunities to violate the facility along the extended segment. I-15 Express Lanes violation rates range between 5 percent and 15 percent, with some time-of-day and seasonal variations.
91 Express Lanes (Orange County, CA)
On the 91 Express Lanes, visual enforcement is performed at three locations where the median was widened to accommodate a vehicle. Flexible delineators separate the Express Lanes from the SR-91 mainline lanes, with no intermediate access locations between the eastern and western entry points of the facility. The entry points have a dedicated HOV3+ lane and an Express Lane. Only eligible HOV3+ vehicles can enter the HOV3+ lane; these vehicles are charged a half-toll.
The Orange County Transportation Authority (OCTA) contracts for enforcement with the California Highway Patrol (CHP), which performs visual enforcement at three locations along the 91 Express Lanes. OCTA reports that the violation rate for the 91 Express Lanes is approximately 8 percent.
MnPass (Minneapolis, MN)
MnPass uses a solid double white line to separate HOT lanes from general use lanes. A dotted striped line indicates authorized access / exit points. According to MnDOT, after lane striping was implemented, there was a drop in the violation rate from over 20 percent to less than 10 percent. Violators of marked striping are fined $165.00 per occurrence.
The enforcement strategy, which was considered critical to the success of the MnPass program, combines visual enforcement with mobile reader technology. It is worth noting that there was very little enforcement of the I-394 HOV lane prior to conversion to MnPass, with violation rates between 20-30 percent. With the opening of MnPass, enforcement was carried out through a partnership with the Minneapolis Highway Patrol, Minneapolis Police Department, and Golden Valley Police Department. Combined, the enforcement contracts cost approximately $165,000 annually.
Enforcement of valid trips is accomplished through three methods:
MnPass has supplemented the violation indicator light by adding a portable transponder reader in the enforcement vehicles enabling enforcement officers to validate operational transponders while driving along side of or immediately behind a target vehicle.
SR-167 HOT Lanes (Seattle, WA)
SR-167 uses an electronic toll collection system that features an in-vehicle transponder, over-roadway transponder readers mounted on overhead gantries, and variable message signs that post the time-of-day toll. Similar to MnPass, SR-167 uses a solid double white line buffer to separate the HOT lane from adjacent highway mainline lanes.
When a vehicle passes through the access point with an active transponder, a flashing enforcement light activates. If the light does not flash, state highway patrol checks to see if the vehicle has two or more occupants. If not, the vehicle is cited with a violation.
The successful operation of a HOT lane facility is dependent upon a visible and effective enforcement program that the public perceives as fair and consistent. For the time being, the ability to deter violations and abuses of the HOV exemption allowance is strongly tied to the visibility of HOT lane enforcement presence. When lane enforcement presence is weak or non-existent, violation rates can rise above the generally accepted range of between 8-15 percent.
The enforcement strategies used HOT by lane operators provide some useful insights on best practices and lessons learned. Below is a summary of key findings:
Accurate, informative signs are essential in explaining operational procedures of HOT lane facilities and ensuring safe access and egress from the managed lanes. HOT signs should provide motorists with information on:
A major element in HOT operations and management is signage, both upstream and downstream of the facility’s ingress/egress points. Inadequate signage can diminish the customer’s ability to make an informed travel decision and may compromise vehicle safety. Often there are possible conflicts between signing for general purpose lanes and for managed lanes. Drivers in both lane types can see not only a message intended for their lane use but can also see the message for the other lanes as well. The signage needs to be such that each driver clearly understands which message should be followed.
Coordination of signage both from a visual and an operational perspective is important. FHWA, in collaboration with the International Bridge, Tunnel and Turnpike Association (IBTTA), recently completed a study of traffic control strategies at toll plazas and issued a report entitled, “State of the Practice and Recommendations on Traffic Control Strategies at Toll Plazas.” The recommendations contained in the report address (1) solutions to improve safety and operations of existing toll plazas; (2) contemplating replacement or modification of an existing toll plaza; or (3) planning a new toll plaza. While potentially applicable to HOT lanes, the report includes recommendations for Advance Signage and the Color of Toll Signs, but does not specifically address HOT operations. Unfortunately, The Manual on Uniform Traffic Control Devices (MUTCD) for Streets and Highways 2003 Edition does not provide a recommendation or standard for HOT signage. Some current toll agencies and other future ORT toll facilities have implemented purple-background signs to differentiate the facility from conventional roadways or other toll facilities. The Harris County Toll Road Authority (HCTRA) uses purple-background signs on their WestPark Tollway in Houston as part of an Experimentation Project (see Section 1A.10 – Interpretations, Experimentations, Changes, and Interim Approvals, pages 1A-4 through 1A-7 of Chapter 1 from the 2003 MUTCD. The MUTCD 2003 Edition does not prohibit such use, but also does not endorse/recommend its use. The two signs below where used for conventional toll plazas, but their color distinctions should be considered as an example to provide unique and distinct HOT signage.
Since SAFETEA-LU failed to fund the development of the 2008 MUTCD, no new recommendations or standards are planned at this time that would include toll roads or HOT lane applications. Until the MUTCD provides standards for toll road or HOT signage, it is recommended that agencies or DOT’s plan to use purple signs, similar to the HCTRA signs used for the WestPark Tollway, and that that application be made to FHWA for an Experimentation Project, similar to the HCTRA project, for use of the purple signs. This will permit the use of the signs, while not officially covered by the MUTCD at this time.
While the MUTCD currently provides no guidance on signing for HOT lanes it is particularly important to have good signage when variable tolls are involved and it is critical in directing motorist to access and egress locations. Although MnPass chose not to use purple for their implementation the figure here is a good example of a distinctive sign that is in use by MnPass on their HOT implementation on I-394. It is clear, easy to understand, and provides the driver with information on the toll and distance to the HOT access. Two additional examples of informative and clear signage are shown in the figures below.
Signage placement must be located at a sufficient distance to provide the motorist with enough time to safely execute the directions provided or to change lane if needed to comply with the signage. The chances for operational success of a managed lane facility will be enhanced by good informational and directional signs.
It is equally important to ensure that signage displaying enforcement provisions for lane violations is displayed consistently and frequently along the HOT corridor. It has been found that the lack of consistent enforcement signage contributes to unauthorized users accessing the facilities.
Additionally, the inadequacy of enforcement signs also appears to contribute to the practice of lane diving from the general purpose lanes into the HOT lanes that are not barrier separated which can create safety hazards.
The sponsoring agency must develop a comprehensive incident management plan to address a wide range of situations that can impact facility operations. For example, if there were a major accident on highway mainlines that resulted in severe backups, should the HOT lane eligibility requirements be temporarily waived to maximize corridor-wide throughput until the accident is cleared? Conversely, if there were a major incident on the HOT lanes and they were to be closed, how should the event be handled? How will necessary information be conveyed and what information should appear on VTMS?
The functional requirements for HOT lanes are best integrated into a region’s traffic operation center. The development of a Regional Incident Management Plan that addresses incident types and mitigation options for each type must be developed and updated regularly. For an Incident Plan to be effective, the plan must be tested and training on the execution of the plans must be performed on a regular basis. If transit operations are integrated in the facility, then transit vehicle incident management must be included in the Incident Management Plan.
With a regional traffic operations center, on-site personnel may be employed to monitor and address traffic incidents and enforce rules and regulations that cannot be addressed remotely. For example, although SANDAG’s I-15 Express Lanes is operated by a private company, incident management is under the sole control of Caltrans, who make decisions to divert traffic from or onto the Express Lanes depending on the nature of the incident. Reversible flow lanes, in particular, must have on-site staffing to ensure safe and efficient opening and closure of lane operation, regardless of the level of automation applied to the deployment of traffic control devices. Typically, staffing resources varies with the amount of automation, but a minimum of one person per peak period needs to drive the lane and make sure all of the traffic control devices are fully deployed in a correct manner.
HOT lanes are increasingly turning to ITS systems to track users, monitor operation performance, confirm whether tolls have been paid, and confirm lane status when incidents occur. The implementation of a basic incident detection system must include automated interfaces, typically with video and incident detection software application to effectively detect incidents and to deal with regional traffic issues in a timely manner.
As soon as the severity of an incident is determined by operations personnel, information on travel options should be posted in real time on VTMS and DMS in the area. If Highway Advisory Radio, (HAR) is included in the region’s ITS suite of equipment, incident alerts should be announced through this medium as well. Along with the message sign and HAR notifications, website posting of separate real-time travel speeds, travel options, and service reliability for the HOV lanes should also be used. In some cities such as Atlanta, Seattle, Houston and Orange County, California, website postings are already occurring, enabling users to quickly assess incident travel options, and available travel benefits between the parallel roadways.
Functional requirements for the HOV/managed lane system should be reviewed periodically as design upgrades in technology and traffic operations management allow.
United States Department of Transportation – Federal Highway Administration
Last Modified: June 30, 2009