65 mph speed limit sign with a background of long exposure trails. - Wirestock Creators // Shutterstock The dangers of raising speed limits on interstates The recent increase in the speed limit on I-465 in Indiana, from 55 mph to 65 mph, raises the question of whether raising the speed limit on highways is a good idea. While the increase is meant to enhance the flow of traffic on the often busy interstate, there are several potential dangers that drivers may not consider.