Freeway Management and Operations Handbook
Chapter 8 – Managed Lanes
|Location / Study||Conditions||Results / Comments|
|Florida I-95, Broward County||Conducted a 6 month, 7 am to 7 pm study in 1988||Public feels safer with lane restrictions for trucks. Overall accidents up 6.3 percent (7 am to 7 pm period); truck accidents down 3.3 percent.|
|Georgia||Beginning Sept. 1986, trucks were restricted to the right lane(s) except to pass or to make a left-hand exit.||On I-285, trucks were at fault in 72 percent of lane-changing violations. Before the restriction, trucks were observed occupying all lanes thus prohibiting passing.|
|New Jersey||Turnpike Authority (NJTA) imposed lane restrictions in the 1960's. Restrictions do not allow trucks in the left lane of turnpike roadways that have three or more lanes by direction.||Sources at the NJTA stated that the compliance rate for truck lane restrictions is very high.|
|Illinois||Began in 1964.||Public feels safer, and better operations.|
|Maryland Capital Beltway||Believes to have been implemented as a reaction to a major truck accident.||Public feels safer. Effects on safety not well known.|
|Virginia Capital Beltway||Four studies, one for 24-months, others for 12 months.||Public and political perception: safer highways. Engineering study recommended removal. Accident rate increased 13.8 percent during 2-yr. Study. Second study also showed increase.|
|Michigan||Statewide restrictions require trucks to use the right two lanes on roadways that have three or more lanes.||Establishment was thought to be politically motivated. No studies available to evaluate the countermeasure.|
|Garber Study||Simulation based on data from nine sites.||Decreased headways in right lane. Slight increase in right lane accidents.|
|Hanscom Study (23)||Two 3-lane suburban sites, all <100,000 AADT.||Beneficial traffic operations and reduced congestion.|
A survey of State practice in 1986 by the FHWA (7) identified the most common reasons given for using truck lane restrictions:
Truck restrictions can be implemented in a number of other ways as well. Table 8-2 (8) summarizes the constraints and impacts of different types of restrictions.
|Driver Training / Certification||
|Increased Enforcement of Existing Regulations||
A recent project in Houston implemented a truck restriction lane on an eight-mile section of the I-10 East Freeway (9). The study reported a 68 percent reduction in crashes over a 36-week period. A truck restriction lane on I-40 near Knoxville resulted in a substantial reduction in the percentage of trucks traveling the left lane even with minimal sign usage and enforcement (10).
Separated roadways for trucks are less common. A well-known example is the New Jersey Turnpike, which features completely separated roadways, one reserved for passenger cars only, and the other open to both commercial and non-commercial traffic. Figure 8-2 shows a dual-dual section of the Turnpike. The data in Figure 8-3 shows that the dual-dual portions of the NJ Turnpike enjoy lower accident rates than the sections where commercial traffic is not separated.
Dedicated roadways for trucks are even less common. One example is the South Boston Bypass Road, a two lane undivided roadway with no shoulders. The SBBR is restricted to commercial vehicles only – including taxis, jitneys, limos, and automobiles with commercial plates. The restriction was instituted to mitigate noise and emissions by siphoning truck traffic from I-93 through an industrial edge of South Boston. The roadway reduces demand on a saturated I-93 through the middle of downtown Boston and usually operates with free flowing heavy truck traffic.
Climbing lanes typically are built to improve operations on grades by separating slow moving heavy vehicles from the rest of traffic. These lanes have become a common practice and AASHTO (11) provides established criteria. Additional information is provided in Chapter 5.
Interchange bypass lanes have been implemented in Southern California and Portland, Oregon to route trucks around a major merge, thereby improving traffic operations at the interchange. Figure 8-4 shows such a bypass lane at the I-5 / I-405 interchange in Los Angeles.
Another form of managed lanes is the dedication of a lane(s) to high-occupancy vehicles only. (For discussion of high occupancy vehicle lanes, see Chapter 9 (High Occupancy Vehicle Treatments).
Entire roadways have been restricted to HOV use on an emergency basis. In the wake of the terrorist attacks of September 11, 2001, New York City required vehicles entering bridges and tunnels south of 63rd Street in Manhattan to have at least 2 occupants (See Figure 8-5). This was to reduce traffic congestion due to heightened security checks of vehicles using these facilities.
Research has confirmed that shoulders and narrow lanes can be used effectively to increase capacity in congested metropolitan corridors. This strategy is discussed in Chapter 5 herein and in Reference 12.
A contraflow lane is a freeway lane in the off-peak direction of flow (normally adjacent to the median) that is designated for use by HOVs traveling in the direction of peak flow for at least a portion of the day (See Chapter 9). They may also be used during major evacuations as discussed in Chapter 12. Normally, the contraflow lane is separated from the off-peak (or opposite) flow by insertable cones, pylons, or movable concrete barriers.
Application of contraflow lanes has been limited to areas of extreme congestion where directional flow imbalance permits their use. This approach is sometimes used as an interim measure during the definition and development of long-range solutions. Table 8-3 describes two contraflow projects in the New York / New Jersey metropolitan area on severely congested approaches to tunnels.
|Lane Characteristics||New Jersey||New York|
|Route||I-495 approach to Lincoln Tunnel||I-495 approach to Queens Midtown Tunnel|
|Length in miles||2.5||2|
|AM / PM||AM||AM|
|Remaining off peak traffic lanes||2||2|
|Typical bus volumes||500/peak hour
|Typical passenger volumes||21,000/peak hour
Disadvantages of freeway contraflow lanes include:
To best use existing facilities, a number of jurisdictions have instituted reversible-lane flow (also known in Europe as tidal flow lanes). Reversible lanes change the directional capacity of a freeway to accommodate peak directional traffic demands. To warrant reversible lanes, peak-period traffic volumes should exhibit or anticipated to exhibit significant directional imbalance (e.g., 70/30 percent, Reference 40). If warranted, reversible lanes can use right-of-way more efficiently and economically. Figure 8-6 illustrates an example of the directional peaks that reversible lanes can mitigate.
Reversible lanes on a freeway have usually been implemented on a roadway cross-section that includes a completely separated set of lanes in the center of the freeway. These are reversed in accordance with peak demands usually on a time-of-day basis.
An example is the set of reversible express lanes (lanes that do not have access to and from all interchanges) on San Diego's I-15 which have been in operation for 14 years. The reversible 2-lane facility is located between the Ted Williams exit (SR-56) to the north and the SR-163 exit to the south. This facility has three operational barrier gates that are open from 5:45 am to 9:15 am for the morning peak inbound, (southbound), and from 3:00 pm to 7:00 pm for the evening peak outbound, (northbound). The I-15 HOV facility uses both lanes in the same direction for each operational period and is open to the following vehicles:
On weekends, the I-15 HOV facility is normally not open / used except in extenuating circumstances. As a result of a managed lanes initiative, the lanes are now open to single occupant vehicles (SOVs) as part of the Congestion Pricing / HOT Lane initiative. (See section 188.8.131.52 and Chapter 9).
In addition to the three barrier gates, the equipment that operates the facility includes pop-up lane delimiters for lane control, video cameras, vehicle detection, lighting, and 12 CMS signs. The configuration is shown in Figure 8-7.
Separated reversible lanes have also been designed and implemented on the Kennedy Expressway in Chicago, Interstates 5 and 90 in Seattle, and the Shirley Highway in Northern Virginia (See Figure 8-8).
The Kennedy Expressway has a 7-mile, two-lane reversible roadway in the median strip. The reversible lanes serve as express lanes and have only one access between their terminals for outbound-only flow. The outer roadways have three to four lanes and operate in only one direction.
Interstate 5 on the northern approach to Seattle has a 7.5-mile reversible-lane section in the median. However, the reversible lanes are not express and have several interchange points. The major features of this system include:
These devices are activated locally at each ramp site. To help motorists become familiar with the system, lane reversal is usually performed at the same time each weekday (with weekend hours varying slightly from the weekday).
Reversible lanes not using a completely separated set of lanes are often used in tunnel and bridge operations for:
The center lane of the San Diego Coronado Bridge is reversible along its 1.6-mile length. The configuration is changed twice a day to accommodate peak hours (3 lanes in the peak direction and 2 in the off-peak direction. It uses a moveable barrier, is deployed Monday through Friday and has been in operation for 10 years.
New York's Tappan Zee Bridge reverses a lane twice a day, changing the center lane from northbound to southbound and back again. This application also uses Moveable Barrier Technology (See section 184.108.40.206).
Reference 15 identifies the following considerations that need to be addressed when considering a Moveable Barrier technology (MBT) application (which are also applicable to any reversible lane / contraflow lane scenario:
Mainline metering controls the mainline traffic entering a freeway section or a limited access bridge or tunnel. While the technique can create congestion on the mainline upstream of the controlled section, it can help maintain uncongested flow on the mainline downstream. While limited applications of mainline metering on controlled access facilities such as bridges and tunnels roads have been found effective, the concept has not yet found application to a typical metropolitan freeway system.
Mainline metering can accomplish the following objectives:
Mainline metering can cause queues on the mainline, which may be met by significant community opposition.
Toll facilities often function as mainline meters. The principal example of mainline metering in the U.S. is westbound I-80 at the San Francisco-Oakland Bay Bridge (16). Shown in Figure 8-9, this installation places the mainline meters just downstream of a 22-bay toll plaza. Westbound traffic approaching the San Francisco-Oakland Bay Bridge passes through the toll plaza and is then metered to narrow the 22 lanes of traffic into four lanes as efficiently as possible. HOV lanes allow HOVs to bypass the traffic queues.
Mainline metering has also been used on one lane at the westbound entrance to the Holland Tunnel in New York City (17). A before and after study concluded that metering improved traffic volume throughput by approximately 7%.
Another potentially effective use of mainline metering that has not yet been applied is in a construction zone where traffic demand greatly exceeds the capacity available, and some reserve capacity for vehicles entering at downstream ramps needs to be provided (18).
Variable speed limits (VSL) are intended to allow reasonable and realistic speeds based on time of day, traffic conditions, weather conditions, construction or maintenance activities, and other factors. With the exception of school zones, use of variable speed limits in the United States has been limited, although many transportation agencies have expressed interest in them. Use has probably not been more widespread due to concerns over their legal basis, the level and type of enforcement required, and the lack of information on proven benefits.
Some static speed limits in dynamic environments have low levels of compliance, and speed limits that are responsive to the situation should be more credible and may result in improved compliance. In other situations, the speed limit may be too high for the conditions, and a variable speed limit could provide additional information that may be beneficial to the driver.
Variable speed limits use traffic speed and volume detection, weather information and road surface condition technology to determine appropriate speeds at which drivers should be traveling, given current roadway and traffic conditions (19). These advisory or regulatory speeds are usually displayed on overhead or portable changeable message signs (CMS) (See Figure 8-10). In the U.S., VSL are deployed in Colorado, Minnesota, Nevada, New Jersey, Massachusetts and Washington State. Often they are part of larger incident management, congestion management, weather advisory, or motorist warning systems.
An example deployment is on the New Jersey Turnpike where enforceable variable speed limit signs have been in use since the late 1960s to provide early warning to motorists of slow traffic or hazardous road conditions. Approximately 120 signs are installed over 148 miles of roadway. The posted speed limits are based on average travel speed and are displayed automatically (manual override used for lane closures and construction zones). The posted speed limit can be reduced from the normal speed limit (depending on the milepost location 65 mph, 55 mph, and 50 mph) in five-mph decrements, to 30 mph. The posted speed limit can be reduced for six reasons: accidents; congestion; construction; ice; snow; and fog. The speed warning signs display, "Reduce Speed Ahead" and the reason for the speed reduction. When appropriate, the distance between the warning sign and the beginning of the congestion is displayed on the warning sign. The New Jersey Turnpike Authority feels that the signs are effective, and provide motorists with information on unusual roadway conditions that dictate the need for speed reduction. State Police enforce the reduced speed limits by issuing summonses to those motorists found to be in violation.
VSL systems have been in use for the last 30 years and currently are successfully being deployed and / or tested in Australia and Europe. An example is the Netherlands' Motorway Control System. It provides lane control and speed limit signs generally every 500 meters and is used to slow traffic either in advance of a slowdown / shock wave or work zone. The system has proven effective in reducing collisions by about 16% (20) and has increased throughput 3–5 percent. It also reduces the cost of work zone traffic control.
Tests are being conducted in Maryland, Michigan and Virginia to determine the effectiveness of Variable Speed Limits in work zones. VSL systems will rely on input of vehicle speeds and other information to post an appropriate speed limit, allowing motorists to maintain the most efficient and safe speeds, without endangering themselves, other drivers, or workers. Each of the selected states will implement VSL systems in a work zone, monitor operations, and evaluate system effectiveness.
A work zone is an area of a highway with construction, maintenance, or utility work activities; it extends from the first warning sign or rotating / strobe lights on a vehicle to the END ROAD WORK sign or the last temporary traffic control device. Within a work zone, safe traffic flow is maintained by providing temporary signage, channelizing devices, barriers, pavement markings, and / or work vehicles. Traffic management in work zones is important to the safety of both workers and motorists. Time is required to properly develop and implement the traffic control when lanes must be closed to complete the work. No one sequence of traffic control devices can be designed for all situations. In addition, a work zone cannot always maintain the same number of lanes and the path through a work zone will be influenced by the traffic control devices present. Where possible the traffic control plan should be designed to provide the same number of lanes of traffic during construction as before. Ideally, the traffic control plan should be designed for the same free-flow traffic speed that existed before freeway construction.
The MUTCD (2) extensively discusses temporary traffic control plans that include temporary traffic control measures for facilitating travel through a work zone. These plans play a vital role in providing continuity of safe and efficient road user flow through a work zone. Temporary traffic control plans can be very detailed or simply reference typical drawings contained in:
The degree of detail in the temporary traffic control plan depends entirely on the complexity of the situation. The selected traffic control plan should have the approval of the responsible highway agency prior to implementation.
In addition to the MUTCD, several other resources exist for planning and evaluating work zone strategies. These include:
The Work Zone Operations Best Practices Guidebook (21) is a resource designed to give state and local transportation agencies, construction contractors, transportation planners, trainers, and others with interest in work zone operations access to information and points of contact about current best practices for achieving work zone mobility and safety. This guide leverages the collection of work zone operations best practices by providing an easily accessible compilation of the best practices in a variety of cross-references, thereby enabling users to find best practices in several different ways, including by:
The best practices are descriptive not prescriptive. That is, they describe approaches used by transportation agencies, along with contact information. Each organization must determine which of these practices are best suited for its particular situation, considering all factors that affect work zone operations.
The Work Zone Mobility and Safety Self-Assessment Guide (22) is grouped into functional categories that deal with the project development processes, such as Leadership & Policy, Planning & Programming, Design, Construction & Operations, Communications & Training, and Evaluation. The performance-rating scheme is based on the classic process improvement approach. It includes 5 stages – Initiation, Development, Execution, Assessment, and Integration. Within each stage there is a High, Medium, and Low performance level to choose from. The results of this self-assessment can provide an indication of how well transportation agencies are doing in mitigating the impact of work zones on congestion and crashes.
Finally, it is emphasized that the concept of work zone management is more than lane management strategies and the set up / configuration of the work zones themselves (i.e., cost-effective mitigation measures to directly handle the traffic impacts encountered during the construction and maintenance operation). The exposure of the motorist and the highway worker can be reduced – thereby also reducing motorist delays and crash rates – through other proactive means, including:
Toll facilities are fully controlled access roadways designed to the same high standards of design as freeways. However, because of both the economic influence they exert on traffic demand for the facility and the traffic metering effect that occurs at the toll collection plazas, toll facilities can also be considered another form of managed lanes. Toll facilities form the most direct user charge for providing revenues based on the costs of travel. Often, they can be implemented more quickly, because the capital funding is available up front and because toll roads often do not have to comply with federal regulations. Also, toll facilities provide a revenue stream for ongoing operations and maintenance.
Legislation has been enacted to facilitate the development of toll facilities through innovative financing. For example, the Federal Highway Act of 1987 provided for eight demonstration projects across the nation, allowing a mixture of toll revenues with state and federal funds on new projects. California enacted legislation that allows the development of joint-power authorities to collect developer fees for transportation projects, and awarded four franchises to private entities, allowing private designing, financing, construction, and operation of toll facilities for 35 years.
Toll road facilities are a means of financing roadway improvements. The intent is to finance roadway construction only if there is sufficient demand willing to pay a premium for services rendered by the facility. Furthermore, the user population must be willing to pay for the opportunity to save time in the system because toll road facilities are generally less congested. The concept of toll roads has proved a realistic procedure to finance the construction of needed facilities. There are several advantages and disadvantages involved in the implementation of toll roads as opposed to free roads. Table 8-4 lists some of the advantages and disadvantages of financing a road via user tolls.
Congestion Pricing (also known as Value Pricing) is a lane management strategy whose use has increased significantly due to the public acceptance and use of Electronic Toll Collection (ETC) technologies (See section 8.2.6). Congestion pricing charges a premium to road users who want to drive during peak periods such as rush hour or holiday weekends.
Travel during congestion costs society more (in terms of increased infrastructure needs, increased emissions and fuel consumption); therefore users during those times should pay more. The most straightforward way to implement congestion pricing is on existing toll facilities if they are congested during certain times of day, much like transit or airline fares are often higher during peak travel times.
Key features of congestion pricing for freeway lane management include:
Benefits of congestion pricing are:
Key issues to address when considering congestion pricing include:
There are logistical, institutional, and attitudinal barriers that must be addressed when implementing a congestion pricing system. A feasibility study must therefore be undertaken prior to implementation. The following tasks should be conducted:
Congestion (roadway) pricing has seen limited use in the United States, though already proven successful in efforts to reduce congestion in Singapore, London, and several Norwegian cities. Implementation of roadway pricing has been discouraged in the U.S. due to technical and political problems. The use of ETC technology overcomes some of the technical barriers such as congestion at toll booths. To overcome political barriers, demonstration projects can be performed to introduce the concept. Congestion pricing should not be introduced on a facility that traditionally has no charge. Two recommended facilities that should be used to introduce this concept are:
A pricing schedule should be designed so that initial costs are fairly low. These costs should be maintained for a period of 6 to 12 months to permit behavior patterns to stabilize, after which the cost should increase. This process should continue until the cost is at the desired level. The use of congestion pricing is expected to improve the traffic flow, ridesharing, and emission-reduction experienced on the roadway. These improvements should be quantified in the demonstration project to prove these benefits.
Table 8-5 presents barriers to the implementation of congestion pricing using ETC technology, and recommended strategies. Three arguments that justify the use of congestion pricing are:
|Congestion and Pricing as an Additional Tax||
One rationale for congestion pricing is that it generates revenue. The facility sells to motorists, on a time-of-day or congestion-level basis, the excess capacity available from operation of HOV or other special purpose freeway lanes or exclusive roadway toll facilities. This concept of High Occupancy Toll (HOT) lanes is discussed in Chapter 9 and Reference 39.
Congestion pricing has gained institutional acceptance as a management tool with the success of toll road and express lane facilities in Southern California. These facilities include: