My information may be outdated, but in the past I've been advised that late night travel on the new Mumbai-Pune expressway is dangerous owing to a large number of vehicles being driven rashly and at excessive speeds by tired and sleepy drivers (and no doubt a fair number of inebriated drivers at the wheels too - a problem all over India on the roads at night) leading to a high number of accidents. And at least as of 2014 there seemed to be a number of robberies reported at night on this highway. All this might have changed, I'm not sure; do check with a knowledgeable local.