Optimal regenerative braking recovers like 2/3 of the energy lost, and suboptimal braking -- for instance, if you need to decelerate more rapidly because of a bend in the road -- is worse.

Every 100 feet of elevation change amounts to ~1% of the battery capacity of a Chevy Volt; a couple of small mountains, with lots of ups and downs, and it's easy to lose 5-10% of your range versus taking a more level route, 5% if you brake well, 10% if you brake poorly.

[Which is not to say that hitting the thruway doesn't also kill your range fast.]