Highway Flashcards

On a two-lane highway, passing sight distance must be sufficient for a vehicle to safely pass another vehicle traveling at what assumed speed relative to the passing vehicle?

Answer: 10 mph slower

AASHTO assumes the passed vehicle travels 10 mph below the design speed while the passing vehicle travels at design speed.

What is the typical maximum grade allowed on an Interstate highway in flat terrain according to AASHTO Green Book?

Answer: 3%

AASHTO limits maximum grade to 3% on Interstates in flat terrain to maintain acceptable level of service for trucks.

The equivalent single axle load (ESAL) concept was developed to compare the damaging effect of different axle loads to which standard axle?

Answer: 18,000-lb single axle

ESAL converts all axle loads to equivalent repetitions of an 18,000-lb (80 kN) single axle load for pavement design purposes.

In traffic engineering, the 85th percentile speed is used primarily for which purpose?

Answer: Setting speed limits

The 85th percentile speed reflects the speed at or below which 85% of drivers travel and is a key basis for setting posted speed limits.

Which drainage structure is typically used to carry highway runoff water under the roadway from one side to the other?

Answer: Culvert

Culverts are enclosed conduits placed beneath embankments to allow stormwater to cross from the upslope to the downslope side of the road.

What does the term 'level of service' (LOS) A represent on the Highway Capacity Manual scale?

Answer: Free-flow speed with low traffic volumes and full driver freedom

LOS A represents the best operating condition: free-flow speeds, very low density, and drivers experience virtually no delay.

In rigid pavement design, which type of joint prevents differential settlement between adjacent slabs while allowing horizontal movement?

Answer: Expansion joint

Expansion joints provide space for concrete slabs to expand due to temperature increases while dowel bars transfer load and prevent differential vertical movement.