Blowing Dust on US-95 With a Slow Truck Ahead
You are northbound on US-95 in open desert north of Las Vegas, posted 70 mph, towing a small utility trailer. Late in the afternoon a wall of blowing dust crosses the highway. Visibility drops to about 150 feet, and the low sun behind the dust makes the pavement ahead look flat and uniform. Roughly 200 feet ahead, a loaded dump truck is moving at about 45 mph in your lane with its taillights on, kicking up more dust from its tires. Oncoming traffic appears out of the haze one vehicle at a time. The paved shoulder is about 10 feet wide. Behind you, a semi has been closing for the last mile. Your brakes, tires and trailer lights are in good condition and the pavement is dry, though dust is settling on it.
1. What speed should you be traveling, and how do you justify that against a posted 70?
Read the worked answer
The posted 70 is a ceiling, not a target. The basic speed law requires a speed at which you can stop within the distance you can actually see - the assured clear distance ahead. With 150 feet of visibility, do the arithmetic:
Assume 1.5 seconds of perception and reaction, and braking at about 0.35 g (generous, since dust on pavement lowers friction).
- 70 mph (about 103 ft/s): 154 ft of reaction plus roughly 460 ft of braking ≈ 615 ft. You need four times the visibility you have.
- 45 mph (66 ft/s): 99 ft plus about 190 ft ≈ 290 ft. Still far too long.
- 30 mph (44 ft/s): 66 ft plus about 86 ft ≈ 152 ft. Still marginal.
- 25 mph (37 ft/s): 55 ft plus about 60 ft ≈ 115 ft. This fits inside 150 ft with margin to spare.
So roughly 25 mph or less, trailer and dust included, is the defensible number. At 70 you would be driving blind for over 450 feet, which is how multi-vehicle dust pileups happen.
2. Should you pass the dump truck?
Read the worked answer
No. Passing here requires three things you do not have.
- Sight distance in the oncoming lane. You need to see far enough ahead to guarantee a completed pass. With 150 feet of visibility you cannot see the oncoming vehicle that is about to materialize out of the haze, and the truck's own dust cloud is doubling the problem behind it.
- A predictable gap. The truck is doing 45; you would be accelerating in limited traction with a trailer attached - the slowest, longest possible pass, held entirely inside a dust cloud.
- A usable escape route. You may be able to duck right, but the 10-foot shoulder is where the dust plume is worst.
Instead: drop back to a gap you can stop inside at your reduced speed, and offset slightly within your lane so you are not staring into the truck's taillights and losing your night vision to the sun. If it gets worse, the correct move is to get off the highway, not to get around the truck.
3. Visibility falls to the point where you cannot see the road at all. What is the correct sequence?
Read the worked answer
This is the pull-aside-and-stop scenario that desert states campaign on, and the details matter because most dust-storm deaths are rear-end and chain-reaction crashes involving vehicles still sitting where traffic expects a moving car.
- Get fully off the pavement, as far right as the shoulder and the ground beyond it allow. Not half-on, not on the fog line.
- Stop. Turn off the headlights and any driving lights - a pair of lights in a dust cloud reads to the next driver as a vehicle still moving in the lane, and people steer toward what they are staring at.
- Hazard flashers on, parking brake set.
- Take your foot off the brake pedal once you are stopped, so your brake lights are not glowing like a car in motion.
- Stay buckled with the seatbelt on and keep everyone inside. Do not stand behind the trailer or walk up the shoulder.
- Wait it out. Dust storms pass; a truck doing 55 in zero visibility does not.
If you cannot leave the roadway at all, that is the one case where staying in your lane with lights on and slowing gradually is preferable to stopping in the traffic lane.