Shimmering pavement, asphalt heat.
Stopped talking in eastern Utah,
after Shelby hit the roadkill and
fritzed the air conditioning. Maybe a
leg, a rib, of an armadillo in the
mechanism. Western Utah,eastern
Nevada, tongues gritty from tasting
the air, sweat pooling in elbows,
anywhere skin touched skin. Gwen
falls asleep driving, car shudders
over the rumble strip, waking both of them with shock, turning their blood to ice.

What techniques does the author use to build tension in this excerpt?