Non-recurrent congestion: How big is the problem? Are traveler information systems the solution?

Recent research on highway congestion has calculated that over 50% of delays are non-recurrent (incident produced). A common inference seems to be that non-recurrent delay constitutes over 50% of the “congestion problem.” But this inference overlooks the fact that non-recurrent delays would not be nearly as large if highways were not already overloaded, and that as travelers respond to changes in non-recurrent delay, additional demand could significantly reduce the percentage gain. Within this paper, the issue of incident delay is examined from the alternative perspective of “effective capacity” (which will be equivalent to the expected capacity over time). When evaluated from this view, strategies aimed at alleviating peak-period, incident-caused congestion (such as Incident Management, IM, and Advanced-Traveler-Information-Systems, ATIS) have only a marginal long-term effect on the average delay of congested highways. The conclusion is that neither ATIS nor IM can be relied on as the solution to peak-period congestion. It is also unrealistic to consider either ATIS or IM as an effective alternative to the conventional strategy of adding lanes and building highways.