Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
Infrastructure Improvements and Demand Optimization
Numerous capacity improvements are available to enhance travel-time reliability. These actions
increase capacity and reduce the sensitivity of the facility to reliability problems. As noted earlier,
on a congested roadway segment, travel time quickly becomes unreliable when nonrecurring
events occur (such as incidents, inclement weather, crashes, and special events). Conversely, when
a road segment is uncongested, travel time can often remain stable - even when nonrecurring
events occur (due to the ability of the roadway to "absorb" these events).
This set of strategies focuses on improvements applied to the roadway environment and optimizing
travel demand. Physical capacity improvements include link additions, lane additions, roadway
widening, access management and pavement resurfacing. Traffic operations improvements include
signal-timing optimization, deployment of intelligent transportation systems (ITS), traffic-demand
metering, and the application of variable speed limits. Strategies related to agency intervention or
guidance include travel pricing and Travel Demand Management (TDM) measures, which focuses
on reducing vehicular travel and promoting alternative travel modes - all measures that are inclined
to improve non-recurring congestion.
Some of the strategies that fall into this category are also considered part of the emerging concept
called Active Traffic Management (ATM). The FHWA defines ATM as “the ability to
dynamically manage recurrent and non-recurrent congestion based on prevailing traffic
conditions. Focusing on trip reliability, it maximizes the effectiveness and efficiency of the facility.
It increases throughput and safety through the use of integrated systems with new technology,
including the automation of dynamic deployment to optimize performance quickly and without the
delay that occurs when operators must deploy operational strategies manually.”
The Advanced Traffic Management approach to congestion management, which has been welldeveloped
in Europe, consists of a combination of operational strategies that, when implemented
in concert, fully-optimize the existing infrastructure and provide measurable benefits to the
transportation network and the motoring public. These strategies include speed harmonization,
temporary shoulder use, junction control, and dynamic signing and rerouting. Managed lanes, as
applied in the United States, are an obvious addition to this collection. In addition, various
institutional issues essential to the successful implementation of active traffic management include
a customer orientation; the priority of operations in planning, programming, and funding
processes; cost-effective investment decisions; public-private partnerships; and a desire for
consistency across borders. (10)
Table 6.6 summarizes the key strategies and the examples presented in this section. The possible
impact on reliability, SWOT, the level of technology involved with each strategy application, and
the possible application to the sources of congestion are noted.
Economic principles suggest that to improve travel-time reliability, travel demand and capacity
will be balance. So, removing bottlenecks eliminates capacity constraints and managing demand
smooths out surges in traffic. To accomplish these two objectives, the mission of transportation
agencies may have to become enlarged. In addition to the mission of economic development and
social access of many transportation agencies, it is likely that demand management will have to be
fully embraced. This will not be an easy task, but it may be a pillar under any scenario to
effectively address reliability problems.
OPERATIONS STRATEGIES AND TREATMENTS TO IMPROVE TRAVEL-TIME RELIABILITY Page 74