Effects on Safety of Pavement- Truck Tire Interaction

DTFH61-85-C-00148A new truck tire tester was built to measure tire forces in braking and cornering under various speed, vertical load, and slip angle conditions and on different pavement surfaces. Six of the most common truck and bus tires were tested. In general, rib tires performed better than lug tires and radial tires performed better than bias-ply tires. Overall, the radial rib tire performed best, both in braking and in cornering, among the six test tires. All of the independent test variables - pavement type, vehicle speed, axle load, and slip angle - have a significant effect on tire traction. The experimental data were processed to derive 48 regression models relating peak and sliding coefficients of braking and cornering friction and critical longitudinal slip to the independent variables. A computer simulation study using the T3DRS, Phase 4 program was also conducted to investigate the effects of suspension type, tire type, roadway alignment, pavement roughness, and surface wetness on truck braking distance. The simulation results showed that trucks may require considerably larger stopping distances than passenger cars

Effect of vegetation on the impact of a severe blowdown in the southern Rocky Mountains, USA

In October 1997, a storm with winds estimated at 200-250 km/h blew down a large percentage of trees in over 10,000 ha of subalpine forest in northern Colorado, USA. In a case study, we analyzed the effect of pre-blowdown tree density, cover-type, and stand structural stage on the percentage of trees blown down. Low tree density led to somewhat lower levels of blowdown than did higher density. Effects of cover-type and habitat structural stage on the pattern of damage from the blowdown varied spatially. At lower elevations, farther from the source of the winds coming over the Continental Divide, aspen forests were less susceptible to blowdown than expected, whereas spruce-fir forests were more susceptible than expected. At higher elevations, closer to the source of the winds, habitat structural stages representing earlier stages of stand development were much less susceptible to blowdown than expected, whereas more advanced structural stages were generally more susceptible to blowdown than expected. Overall, the effects of density, composition, and structural stage on the pattern of damage were modest, but evident. That there is a detectable effect of vegetation composition and structure across this large blowdown implies that, even during extreme wind events, vegetation can influence the extent and pattern of damage, more strongly so in some places than in others. © 2002 Elsevier Science B.V. All rights reserved