Guide Signing for Two-Lane Exits with an Option Lane

In recent years U.S. freeways have seen an increase in the number of exit ramps that feature a two-lane exit with an option lane. This is a situation in which motorists in the rightmost lane of the freeway must exit, and those in the adjacent lane may either exit or continue on the mainline. Communicating information to the motorist about this type of exit is exceptionally difficult. Ideally, a sign should convey the following: (a) If you stay in the right lane, you will be forced to exit. (b) If you wish to exit, you may do so from either the right lane or the adjacent lane. (c) If you are in the adjacent lane and wish to continue on the mainline, you need not change lanes. Making all of these discrete concepts obvious in a simple sign is challenging, and there is no standard sign design for this situation in FHWA's Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). As a result, at least eight different sign designs are being used throughout the United States. This paper presents the results of an NCHRP human factors study conducted to identify the best design for a guide sign for this type of exit. Four candidate sign designs were evaluated with 96 test subjects in a driving simulator. Measures of effectiveness included the number of missed exits and the number of unnecessary lane changes. On the basis of the study results, one of the four designs is recommended for inclusion in the MUTCD.