Maximizing Legibility of Traffic Signs in Construction Work Zones

The Wisconsin Department of Transportation contracted with Marquette University to research improvements in construction work zone signs. The RIGHT/LEFT LANE CLOSED and ROAD CONSTRUCTION series were selected because they are the most difficult to improve without increasing sign size above a 48-in. diamond. All signs used high-intensity retroreflective material. Twelve test signs were selected for day and night viewing by 46 observers under age 65, and 38 observers aged 65 and over. Experimental messages included rearranged legends (three to four lines) substitution of WORK for CONSTRUCTION, 18% stroke width increases on the inside of letters without increasing letter width, and use of Series E letters upper and lowercase [instead of all capitals as required by the “Manual on Uniform Traffic Control Devices” (FHWA, 1988)]. The conclusion of this study was that few improvements can be made in the LANE CLOSED series without more drastic changes than those tested. In the ROAD CONSTRUCTION series, substantial improvement can be made by substituting WORK for CONSTRUCTION and increasing letter size. The 18% stroke-width concept resulted in no improvement and some reduction by day for younger observers. The most promising finding is the improvement possible with Series E letters because of their 20% increase in stroke width. Less loss of night legibility distance compared with that of day occurred with this alphabet than with any other. Further research substituting tenths of a mile for feet, which would allow larger letter size, is recommended, and field experimentation with Series E letter series under Federal Highway Administration requirements is recommended.