Non-recurrent Congestion: Incident Information to Motorists

Abstract

Chapter 4 discussed delay reduction resulting from reduction in the response time to incidents. This chapter describes the other significant ITS approach to mitigating non-recurrent congestion, namely providing motorists with information. Since messaging policies and diversion effects for recurrent and non-recurrent congestion may be different, these subjects are covered in two different chapters.

Motorist information can mitigate non-recurrent congestion in the following ways:

• Induce a motorist traveling on the freeway to divert in the event of an incident. Circumstances that induce diversion include:

  • Capacity reducing incidents on the freeway on which the motorist is traveling or on freeways that are accessed by the freeway on which the motorist is traveling.

  • Capacity reducing incidents and construction for special events on remote facilities. Avoiding the incident on the remote facility may require the motorist to modify his route on the facility that he is currently using.

• Prior to the start of a trip or early in the trip, induce a motorist to change his travel mode or the start time of his trip.

• Make the motorist aware of unusual conditions such as incidents, lane blockages and lane closures. Accidents are reduced by facilitating the motorists’ earlier preparation for these events.

Section 3.1.4 discusses the general issues relating to diversion resulting from non-recurrent congestion and shows several diversion curves. It also discusses policy issues related to motorist information for non-recurrent congestion. The following topics are covered this chapter in connection with diversion to avoid incidents:

• The techniques for communicating with motorists.

• Strategies and policies or developing messages and the use of the content and the strength of the message to influence the percentage of motorists diverting.

• Semi-automatic and manually implemented strategies for controlling diversion.

• The effect of diverted traffic on alternate routes.

• Models for delay reduction resulting from diversion for the diverted traffic, non-diverted traffic remaining on the freeway and corridor traffic.

• The effect of diverted traffic on alternate routes and the necessity for controlling the impact.

The chapter provides guidance and some simple models to assist the engineer in locating dynamic message signs. The importance of the quality of motorist information is discussed, and a simple evaluation measure is provided. The use of ITS for emergency evacuation is introduced and a model for generating and disseminating information is discussed.