Photo courtesy of Garrett via Flickr/Creative Commons license.
The Congestion Management Process (CMP) is a tool to support development of the Regional Transportation Plan and the Transportation Improvement Program for the Wasatch Front Regional Council (WFRC). The purpose of the CMP is to identify congestion reduction needs and to determine whether or not congestion relief can be achieved without additional roadway capacity. The CMP network includes freeways, principal arterials, and minor arterials. Roadways classified in the WFRC travel demand model as collectors, locals, or centroid connectors are not part of the CMP network.
For additional information regarding congestion management, please contact Kip Billings.
The CMP uses two performance measures to identify congestion trends and congestion intensity. Congestion trends are tracked from year to year using the Travel Time Index (TTI), which is the ratio between peak period travel time and free flow travel time. Congestion intensity is measured for each segment in the travel demand model using Vehicle Delay per Lane Mile (VDpLM), Vehicle Delay is the product of traffic volume and delay, and delay is the difference between observed travel time and free-flow travel time. Lane Miles is the product of segment distance and the number of travel lanes.
A series of interactive maps of TTI and VDpLM for 2050 traffic conditions were prepared for the Ogden-Layton and Salt Lake City urbanized areas. Select the “layers” icon at the top of the menu bar at the left to view any of the four maps:
- CMP Network (v9.1.0)
- Top 10% TTI Reduced
- TTI>2.0 or TTI 1.4-2.0
- Top 10% VDpLM
Travel Time Index (TTI) discussed above was used to identify the most congested segments for arterials and freeways. The Congestion Management Report includes a series of maps in Figure 1a and Figure 1b illustrating the increase in congested segments from now to 2050. The maps are for three scenarios: current conditions (2023), the implementation of all the transportation projects identified in the approved TIP (2028), and finally for the 2050 “No Build” scenario which assumes traffic demand and no further transportation improvements beyond the 2028 TIP projects.
WFRC encourages Transportation System Management and Operation (TSMO) strategies for all programmed projects at the planning stage and also the implementation stage. A project orientation meeting is held as each WFRC-administered project reaches the implementation phase. System management and demand management strategies suitable to the project are identified and discussed. For long range planning, operational improvement projects are included in the RTP which references the Congestion Management Report for recommendations. Congestion strategies include HOV/HOT lanes, transit service, ramp meters, ridesharing, active transportation, land use management, innovative intersection designs, and many others.
To identify highway segments needing increased capacity, a “no-build” network is established, including existing highways, approved Transportation Improvement Program (TIP) projects, future transit and active transportation improvements, a 7%-27% increase in freeway capacity for connected and automated vehicles (CAV), and a 15% reduction in home-based work trips due to telecommuting. This modified network, called the CMP network, is modeled with 2050 socio-economic data to pinpoint future congestion areas.
Congestion on the 2050 CMP network is measured by the Travel Time Index (TTI), which is the ratio of peak travel time to free-flow travel time. Proposed Regional Transportation Plan (RTP) projects are overlaid on a map of the CMP network displaying TTI for each segment. Capacity-increasing RTP projects with a TTI greater than 1.4 are deemed eligible to alleviate future congestion. Locations with a TTI over 1.4 but no proposed capacity project are considered potential RTP projects.
The interactive maps in the CMP Report for congestion management include a map of the roadway segments in the top 10% of Vehicle Delay per Lane Mile (VDpLM). Arterial and freeway segments are evaluated separately due to their unique function and operating characteristics. The top 10% of VDpLM is useful to prioritize congestion needs, but is not the only consideration in selecting congestion relief strategies and locations. In some cases, other project priorities such as safety or growth may place a high priority on a particular project. In these cases, the VDpLM data and map are useful to identify needs for congestion relief as well.
After the CMP process, RTP projects are also evaluated against volume threshold standards based on facility type, with guidance provided for daily thresholds, number of lanes, and potential widening for collector, minor arterial, principal arterial, and freeway facilities to accommodate 2050 traffic. RTP prioritization for capacity increasing projects also considers costs, operational improvement strategies, current and future land use, volume to capacity ratio, and system connectivity.
WFRC prepared a “Before and After” report to measure the congestion relief effectiveness of recently implemented projects. The report relied on travel time data from the UDOT Clear Guide system to evaluate travel time improvements from projects started and completed within the 2019 to 2024 timeframe. Not unexpectedly, widening projects, which are often high investment projects, were the most effective in reducing travel time. A more cost-effective investment to reduce travel time was observed with intersection improvements, although the improvement was sometimes difficult to isolate and measure with the tools available. Chokepoint projects were helpful to reduce congestion in some cases, although isolating the congestion was sometimes difficult; and these bottleneck projects also offer safety and operational benefits.