Congestion on urban freeways often creates a need to increase freeway capacity by adding an additional lane. Although adding a lane by widening the existing roadbed is often difficult and expensive, restriping the traveled way with narrower lanes, converting all or part of the shoulder to a travel lane, or a combination of both often is a practical solution. An observational before-and-after evaluation with the empirical Bayes method was done to examine the safety effects of projects involving narrower lanes or shoulder conversions on existing urban freeways in California with four or five lanes in one direction of travel. The evaluation found that projects converting four lanes to five lanes resulted in increases of 10% to 11% in accident frequency. Projects converting five lanes to six lanes resulted in smaller increases in accident frequency. These increases in accident frequency may be the result of accident migration caused by relocation of traffic operational bottlenecks.

Emphasis on work zone safety and improving the identification of work zone problems has been increased by recent legislation and federal programs. There is a critical need for better data related to highway work zone safety. Results are presented of an investigation to (a) determine what is known about the magnitude of highway work zone crashes, (b) examine characteristics of highway work zone crashes using the Highway Safety Information System, (c) investigate how work zone accidents are reported on police accident report forms and within state accident report systems, (d) identify critical voids in the knowledge of the relative safety of work zones, and (e) examine possible ways to address unfulfilled information needs related to work zone safety. Deficiencies of data reporting practices and issues of data needs pertaining to work zone safety are discussed. Recommendations to improve data collection and fulfill information needs are presented, including suggested data elements to be added to police accident report forms.

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