Why do engineers blast through hills instead of building highways over them?

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Can’t get back to all the comments, thanks all <3

EDIT: I used HILLS and not MOUNTAINS on purpose lol, c’mon guys I’m not *that* clueless. Tunnels absolutely do not figure into my question. Thank you everyone for answering this has been enlightening.

EDIT 2: I don’t think it has occurred to some browsers of this sub that the people asking these questions have probably considered their own question and come up with hypotheses already. Trust me, I had 2 hours longer to drive and think after I posted the question at a gas station haha. has confirmed some of my hypotheses about this and also added many new pieces of information to the puzzle which I am grateful for. Some of you taking time out of your day to say “stupid question” or something along those lines, please don’t consider becoming teachers, and go forth in this sub operating under the assumption that a lot of the questions asked here are not just asked out of curiosity, but also just seeking confirmation of hypotheses before going out into the world and spewing BS lol.

In: Engineering

17 Answers

Anonymous 0 Comments

I actually work for a company that build roads in mountainous region. Besides economics, there are few other reasons

1. Weather – there are mountains where it snows all year round. It becomes unmanageable in winters and these kind of roads are usually closed for 5-6 months during the winter.

2. Safety – some hilly roads are prone to mudslides and avalanches.

3. Time – roads in mountains take a lot of time to traverse, if the road is an important connection between two points, usually a tunnel can decrease the time by hours.

Anonymous 0 Comments

Many roads are built to be “more level” to save fuel and meet modern fuel economy standards. Or so I once heard.

Railroads in my area are so much more level than the roads next to them. Hilarious to see actually.

Anonymous 0 Comments

Too steep. My dad had to excavate the entire tip off of a hill because cars would stall trying to climb it. Had to rebuild the entire highway after he cut the hill down

Anonymous 0 Comments

My ex boyfriend in NZ used to bitch and moan all the time about how the roads there snake around mountains when places like Switzerland get all those neat tunnels going straight through, it’s just cheaper though

Anonymous 0 Comments

Lots of good and right answers here. I’ll just add that if an engineer can achieve something equally with an explosion or using other means, he will choose the explosion.

Just sayin’

EDIT:

OK OK… I’ll be honest… explosions will be used when possible. Its just so cool!

Anonymous 0 Comments

Its cheeper to blast hill tops for back fill. You need both cut and fill to prep for a road so they are able to use the environment around the road to make a better road.

Anonymous 0 Comments

The composition of the landscape is also a factor. It’s a lot easier to blast through loose earth and hills than it is solid granite or sedimentary layers like shale that won’t be structurally sound even after reinforcement.

Spent my childhood in Colorado and western South Dakota. You’d be AMAZED at the number of crazy roadways when a “simple” tunnel would suffice.

Anonymous 0 Comments

Great easy-to-understand treatment about road design in general: https://youtu.be/9XIjqdk69O4

He addresses your specific question beginning at about 7:55.

Anonymous 0 Comments

Come to California, where because of earthquakes we build over mountains instead of through them. Everything takes longer and the roads are shittier and more difficult to drive.

Anonymous 0 Comments

Weather and ice conditions will also play a role. Even if the hill isn’t too steep it can be an unnecessary slope in an area with terrible winter driving conditions. The hill can be moved, an idiot cannot be taught how to drive on ice. Ft. Worth taught us that recently