A dun-colored jeep drove up to the stone marker and stopped. It was followed by a strange, tread-equipped vehicle that moved much more slowly. There were toy-sized radar dishes mounted on the front and back of this halftrack. Two soldiers lounged on its upper deck, and Garraty felt a chill in his belly when he looked at them. They were carrying army-type heavy=caliber carbine rifles.
The long walk.
I think 'tread' here means "The part of a wheel or tire that makes contact with the road or rails.". But I'm not sure what "tread-equipped vehicle" really is or looks like. Any ideas?