How Can Bottlenecks be Identified and Assessed?
The first step in bottleneck remediation is identifying bottleneck locations and the root causes of the bottleneck. When multimile corridor congestion is prevalent, travel demand models can assist in identifying, separating, and analyzing bottleneck dynamics within the corridor. Traffic analysis tools can mathematically identify the problem areas by analyzing road segments for congestion or poor level of service. Freeways with traffic detection use archived data to identify where and how often bottlenecks occur, and how severe they are. Historical data is used to track if the problem is growing or receding.
Determining the root cause of the bottleneck can be accomplished with a range of tools. Special travel-time runs and videos of areas suspected to be bottlenecks can be used to pinpoint deficiencies. Microsimulation tools can provide a detailed analysis of the specific attributes of the bottleneck(s) and can assist in determining the impacts of alternative solutions. When conducting bottleneck analysis, care should be taken to ensure that:
- Improving traffic flow at the bottleneck location doesn't just transfer the problem downstream – the existing bottleneck may be “metering” flow so that a downstream section currently functions acceptably, but the increased flow will cause it to become a new bottleneck.
- Future traffic projections and planned system improvements are inclusive in the analysis. Safety merits also should be strongly considered.
- "Hidden bottlenecks" are considered. Sometimes, the queue formed by a dominant bottleneck masks other problems upstream of it. Improving the dominant bottleneck may reveal these hidden locations. It is important to take into account the possibility that "hidden bottlenecks" exist at the analysis stage.
- Situations not traditionally considered by models are included. There are several bottleneck problems, i.e., certain types of geometrics and abrupt changes in grade or curvature that can’t be analyzed by analysis tools. "Engineering judgment" will need to be exercised to identify those problems and possible solutions.
- Planning and operating agencies all agree on problems and potential solutions. Coordination is needed so that bottleneck improvements can be woven into agency programs and the necessary funding is secured.
