The purpose of this study was to characterize respirable dust, crystalline silica, diesel, and noise exposures to construction workers on a large highway construction project in Boston, Massachusetts. The study primarily focused on operating engineers and laborers, and to a lesser extent on ironworkers and carpenters during the tunnel finish and cut and cover stages. Full and partial shift noise dosimeter measurements were collected. Eighty percent of the 40 noise measurements were at or above 85 dBA, with the operating engineers averaging 91 dBA. Sample collection for respirable dust, crystalline silica, and diesel particulates measured as elemental carbon was done using cyclones and personal cascade impactors. Exposure to respirable dust ranged from 0.06 to 21.77 mg/m3 for the 77 workers sampled, with the laborers having the highest mean concentration of 2.85 mg/m3. The respirable quartz measurements for the 32 samples collected ranged from the detection limit of 0.008 mg/m3 to 1.64 mg/m3, with the highest mean concentration of 0.31 mg/m3 attributed to the laborers. The use of drills, when compared to other machine types, produced the highest exposures to respirable quartz. The levels for elemental carbon ranged from 4 to 178 micrograms/m3 (mean of 41 micrograms/m3) inside enclosed work spaces, compared with 0.5 to 53 micrograms/m3 (mean of 10 micrograms/m3) for samples collected in unenclosed work sites. Statistical modeling of the factors influencing the elemental carbon exposures showed that machine type, worker distance from the diesel source, the number of other diesel sources in the work area, and site enclosure were all significant exposure determinants. The results indicate that high exposures to noise, respirable dust, and crystalline silica are common in the highway construction industry.