Mars is my Destination by Frank Belknap Long

We stayed silent until the tractor had rumbled past eight or ten of the breaks in the Big Grayness. They were shrouded in dusk-light now, with no kids playing in the front yards of the housing area pre-fabs. Then, just as we were turning into the clear-away that branched off from the one I'd taken on leaving the hospital, Hillard shouted: "We've got to get over to the left! There's an ambulance right up ahead!"

I heard the siren before I saw it, a banshee-like wail cutting through the twilight, unnerving in its shrillness. It took a moment or two for its winking red headlights to come sweeping toward us and if Hillard had seen them before that it had to mean he had exceptionally sharp eyesight.