Strengthening Linkages between Transportation Demand Management and Traffic Management

Context 1. Managing Demand and Traffic During Weather Events and Natural Disasters

More and more often, major weather events are wreaking havoc on transportation infrastructure and making it difficult or people to get around. Roads and mass transit (e.g., subway and rail) infrastructure can become flooded, covered with snow (figure 3), or blocked by debris, or can experience electrical outages and prevent limited or all travel. These issues are not problems that can be solved in hours—they often take days of cleanup and disruption of any normal schedule. And when mass transit is impacted, often a traveler's immediate solution is to jump in a personal vehicle.

If traffic management and TDM can present a more cohesive set of choices to the traveler, travelers are more likely to make more informed decisions about their travel modes, routes and times. For example, in New York City, in response to a hurricane in 2012 that caused flooding in many subway tunnels and shut down most subway operations for several days (figure 4), the city implemented high-occupancy vehicle (HOV) requirements on all of the bridges leading into the city. The purpose of this strategy was to mitigate the high volume of cars that were anticipated, given the absence of a mass transit option. Knowing this strategy, New York City TDM managers immediately worked with their contacts to communicate this policy change and encourage carpooling options, and enact contingency plans for enabling teleworking options. By knowing about this policy change in advance, TDM managers were able to construct a message to their employer contacts so that employees could be presented with teleworking opportunities as the first option.

As TDM managers and traffic managers continue to consider weather impacts on travel, they may have opportunities to collect better road data or traffic sensor data, especially on local roads or countyroads. These types of data could help with analysis or predictions of how weather may impact localtravel patterns, and help TDM managers and traffic managers think about how to manage demand.

The two case studies presented under this context show how important it is to implement traffic management strategies alongside TDM strategies to help travelers get around when weather has caused major disruptions on a transportation system. For both examples, it was imperative to:

• Disseminate the proper information quickly and through many sources (website viewership often jumped following a weather event).
• Find many and various ways to mitigate the initial reaction of travelers to use their personal vehicle by offering several alternative modes.

Case 1. Hurricane Harvey Mobility Response — Houston Transtar

Leveraging TranStar and interagency partnerships for accelerated and coordinated information dissemination and traffic management in a rapidly changing situation

On August 25, 2017, Hurricane Harvey made landfall at San José Island, TX, as a category4 storm. Over the following week, the storm caused catastrophic damage along the coast of Texas and Louisiana, including widespread flooding across the Houston metropolitan area. Some areas received over 40 inches of rain, hundreds of thousands of homes were flooded, more than 30,000 people were displaced, and over 500,000 vehicles were destroyed by the storm.⁽⁴⁾

The breadth of flooding that occurred in the Houston area during Hurricane Harvey had widespread impacts on mobility in the region. At the height of the hurricane, over 500 State roadway closures created major challenges to public safety and mobility (figure 5). Taking advantage of existing partnerships and both the Houston TranStar (www.houstontranstar.org) and DriveTexas (www.drivetexas.org) websites, TranStar was able to provide real-time closure information to the more than 6 million residents in the region. The information was critical to public safety and mobility, and supported emergency responders throughout the event.

Interdepartmental Coordination

The four agencies of the TranStar partnership each played unique roles in making sure residents received the crucial information needed to make their way safely around:

• The Texas Department of Transportation is responsible for the following operations: freeway operations, intelligent transportation systems design and special projects, media contractors, tolling support operations for SH 288, and transportation management systems.

• The City of Houston has sections of departments working from TranStar to support transportation and emergency management: the Traffic Signal Section, the Police Command Section, and various other key personnel.

• Harris County, which covers 1,788 square miles, has several departments working from TranStar: the Traffic Signal Section, the Sheriff's Office Motorist Assistance Patrol Unit, the Office of Homeland Security and Emergency Management, and the Office of Emergency Management.

• The Metropolitan Transit Authority of Harris County (METRO) has been providing the mass transit operations for the Houston region for many years. METRO has helped TranStar become a truly multimodal operation, with three operational sections conducting business at the center: HOV Operations, Police Dispatch, Bus Operations, and Rail Operations. METRO also supports TDM by providing the most up-to-date storm impact estimations and advice to METRO, which is responsible for orchestrating the region's vanpool program of nearly 6,000 users.

Strategies Providing Route Choice

The primary challenge during the flooding was a lack of road closure information on county roads off the State system. The team held daily conference calls to document flooded roadways, and then TranStar and DriveTexas uploaded that information to their sites to communicate information to the traveling public and emergency personnel. The team also communicated with media outlets about the flood conditions and how they were expected to impact travel.

Successes Supportive of the Integration of Transportation Demand Management and Traffic Management

The TranStar partnership had the following successes:

• The real-time road closure information likely contributed to minimizing the number of deaths on flooded roadways. Traffic to the Houston TranStar website far exceeded that experienced for previous flood events. Usage topped 3 million unique users during the 12-day period, with a peak of over 30 million visits compared to 4 million during a typical time frame. Sometimes, the public agency's website is the source that the public trusts and uses, so the information on such a website can and should provide the information the traveling public needs, especially if the ideal scenario is a shift to non-single-occupancy vehicle modes.

• The extensive communication with media outlets about flood conditions likely increased the exposure of Houston TranStar and the availability of traveler information on its website. It is likely that exposure will encourage citizens in the region to think of TranStar first when looking for traveler information in the future.

Case 2. Utah Department of Transportation's Traffic Operations Center Use of Proactive Messaging During Weather

Sharing anticipated weather information to traveler information leads to shifts in travel behavior Utah has a mixture of remote roads and population centers, and a medley of extreme weather situations throughout the year. To manage the many different types of roadway warnings into a cohesive management system, the Utah Department of Transportation (UDOT) uses its Traffic Operations Center (TOC), a suite of 150 variable message signs (VMSs), social media, UDOT's website, and 511 phone service. UDOT developed a sophisticated system that identifies real-world conditions and events and then translates them into useful messages that can alter travel behavior. A traffic control room manager heads UDOT TOC and oversees the control room operators. These operators actively monitor traffic conditions and implement real-time messaging on current and forecasted road conditions. UDOT has a close relationship with the National Weather Service (NWS) to integrate weather impacts into its traffic analysis. An established VMS policy governs all VMS messages.⁽⁶⁾ VMS messages are locally tailored and include predictive warnings and route guidance (figure 6). Messaging is used frequently in advance of high traffic demand periods and extreme events as a means to mitigate and disperse traffic, both geographically and temporally. Historically, the messaging has also been engaging and humorous to capture drivers' attention.

Through its proactive messaging strategies on its various platforms, TOC has helped move travel demand to times before or after anticipated bad weather, thereby mitigating the worst possible congestion during major events. Various studies have seen that travel demand has shifted to avoid disruptive weather events, such as analysis showing a 40 percent volume decrease at a peak time.⁽⁸⁾ Previously, NWS had operated independently, sometimes creating incongruous messaging to motorists. Now, NWS actively collaborates with in-house UDOT meteorologists to provide clear, consistent messaging about weather-related road conditions.

As a first step in the process of posting VMS messages, UDOT hosts a TOC weather briefing with 10–30 operational managers one to three days prior to every major event. Following the meeting, the weather program manager, control room manager, and travel information manager decide on an exact course of messaging, tailoring messages to specific areas. TOC also leverages a robust signal timing program to guide traffic and optimize traffic flow. The vast majority of signals are connected with fiber, allowing for real-time adjustments, which are controlled by TOC. Since the incident monitoring, weather monitoring, VMS posting, and traffic signal timing adjustments are all run out of the same office, the process to translate conditions into immediate messaging and signal adjustments is very streamlined.

Strategies Providing Destination Choice

By alerting users of when adverse weather conditions will be at their worst, UDOT may convince travelers to stay off the roads entirely or choose an alternate destination. Pre-event messaging is disseminated in the days and hours leading up to events such as snowstorms, thereby encouraging people to stay off the roads during the event. Figure 7 shows an example message that encourages travelers to stay home if possible.

Strategies Providing Time Choice

VMS pre-event messaging is even used on a local scale to help make routing decisions. For example, messages are posted on roadways leading to ski destinations to encourage visitors to leave before an afternoon or evening storm arrives.

Strategies Providing Route Choice

Messages are sometimes simply vague guidance or information for the traveler to consume but sometimes go so far as to recommend specific alternate routes that travelers should take.

Successes Supportive of the Integration of Transportation Demand Management and Traffic Management

UDOT had the following successes:

• The UDOT executive director trusts TOC to successfully determine and implement DMS strategy, which allows TOC to move quickly without waiting long for buy-in.

• Having meteorologists on UDOT's staff allows for faster and more reliable weather information, thereby improving messaging.⁽⁹⁾ This also hastens the process of turning weather forecasts into directives for maintenance staff.

• Pre-event DMS messaging is used frequently in advance of high traffic demand periods.