A result of the proposed introduction of Electronic Motorway Tolling is likely to be the diversion of traffic from tolled motorways to alternative untolled roads. Theoretical issues are considered and the effects evaluated using a single-link accident model which comprises a single motorway link and a single diversion link. Results indicate that a 10% diversion rate would lead to an increase of one fifth in the number of fatal and serious accidents (relative to the original number on the motorway). This basic model, however, excludes several important aspects, such as the likelihood that diversion routes will normally be shorter than the original routes, but will often pass through built-up areas. It is also clear that the consequences for accidents will depend on local road network conditions, making it more difficult to draw national conclusions. The change in the number of accidents that might result from the introduction of motorway tolling depends on network effects that are difficult to reproduce with a single-link model. More reliable assessments can be achieved by using the MCONTRM traffic model with representative networks. (A) (This report is also included on the TRL CD-ROM entitled "Research on road user charging 1995-1998"). For the covering abstract see IRRD 491340.

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