Most of the original interchanges in Florida all cross over the intersecting roa

[roadman65]

I was noticing that a great number of interchanges along I-95 and I-75 have the intersecting road cross beneath it rather than over them.  Matter of fact it was all the original interchanges pretty much as the one's today we see where the roads go over are added interchanges in many places.

A perfect example would be Palm Coast Parkway, LPGA Boulevard, Port St. John, FL Route 404 for I-95 which all have overpasses carrying the exiting roads over I-95 which were all added long after the interstate was built.  Then all the original interchanges (that all had whole numbers before the mile based numbers came) are all with I-95 going over the other roads.  US 92, FL 40, US 1 (in all locations), FL 206, etc.

Then for I-75 the Laurel- Nokomis interchange near Venice is the only interchange south of Tampa and North of Naples where the road crosses over I-75 and that one was added sometime in the early 90's, so it would mean that every interchange on I-75 between those two Florida cities was all where the freeway crossed over each time.

I was always wondering why that was, yet I-4 and the northern part of I-75 north of Gainesville have either or set up with a good mix?  I can see metro Miami having overhead roads at interchanges at that point due to area concerns in suburban areas, which is why that is on the home stretch into FL 826.

[hotdogPi]

I-93 in New Hampshire is similar (except near the MA and VT borders). Almost all of the roads go under I-93.

[jwolfer]

I was noticing that a great number of interchanges along I-95 and I-75 have the intersecting road cross beneath it rather than over them.  Matter of fact it was all the original interchanges pretty much as the one's today we see where the roads go over are added interchanges in many places.

A perfect example would be Palm Coast Parkway, LPGA Boulevard, Port St. John, FL Route 404 for I-95 which all have overpasses carrying the exiting roads over I-95 which were all added long after the interstate was built.  Then all the original interchanges (that all had whole numbers before the mile based numbers came) are all with I-95 going over the other roads.  US 92, FL 40, US 1 (in all locations), FL 206, etc.

Then for I-75 the Laurel- Nokomis interchange near Venice is the only interchange south of Tampa and North of Naples where the road crosses over I-75 and that one was added sometime in the early 90's, so it would mean that every interchange on I-75 between those two Florida cities was all where the freeway crossed over each time.

I was always wondering why that was, yet I-4 and the northern part of I-75 north of Gainesville have either or set up with a good mix?  I can see metro Miami having overhead roads at interchanges at that point due to area concerns in suburban areas, which is why that is on the home stretch into FL 826.

I remember noticing this when I was a  kid. I thought about it and my explanation was when the interstates were new construction is was less disruption to traffic flow on existing roads and no need to relocate roads.

But interestingly the roads that did not have interchanges went over the interstate.

[realjd]

When building the interstates, why tear up an existing road to make a bridge when you can just run the new freeway over top? Thats why the interstates in FL go over most roads that were preexisting but most new roads go over the freeway.

[Fred Defender]

When building the interstates, why tear up an existing road to make a bridge when you can just run the new freeway over top? Thats why the interstates in FL go over most roads that were preexisting but most new roads go over the freeway.

No argument with the logic. But it is not 100 percent correct.

For example (one of many - but the only one that I am 100% certain of):

SR72 in Sarasota. I-75 crosses SR72, but not over the original alignment of SR72 which ran south of its current location.

Also, I-75 crosses both Jacaranda Blvd (fka, Everglades Pkwy, fka, Venice East Road) and River Road. Neither of these two roads existed prior to the construction of I-75. Well, River Road did exist, but not north of Venice Farm Road (Venice Avenue).

I currently live in North Florida (Alachua County). The topography in this part of the state, I'm sure, dictated which roadway went over and which went under. Take, for instance, Exit #404 (Alachua CR236). It would have been impractical, if not impossible, to have built 236 UNDER I-75. Also, I-75 crosses over SR235 and CR2054 south of Exit #399. SR235 has an adjacent railroad track and CR2054 used to also have a parallel railroad prior to the R/R abandonment in the 1970's. This would have made it impractical to have had these roads cross over the interstate.

Prior to 1977, there was no exit at SR24 in Gainesville. This road, like the aforementioned roads to the north, also had a parallel railroad when the interstate was built.

[mhh]

In most cases the freeway will carry much more traffic than the intersecting road. When topography permits, it makes sense to keep the freeway level so the majority of the traffic will have less hill climbing and better forward visibility at high speeds. When heavy trucks lose speed going up slopes, it can create a hazard for cars behind them.

[Fred Defender]

In most cases the freeway will carry much more traffic than the intersecting road. When topography permits, it makes sense to keep the freeway level so the majority of the traffic will have less hill climbing and better forward visibility at high speeds. When heavy trucks lose speed going up slopes, it can create a hazard for cars behind them.

Makes sense. But it doesn't explain roadman65's observation that the interstates cross most of the intersecting roadways when there is an exit involved. Why not the other way around?

Interestingly, heading north on I-75 into Georgia, a great many of the interchanges north of the border cross the secondary roadway OVER the interstate (assuming no co-located railroad - i.e., Exit #16).

[FLRoads]

Then for I-75 the Laurel- Nokomis interchange near Venice is the only interchange south of Tampa and North of Naples where the road crosses over I-75 and that one was added sometime in the early 90's, so it would mean that every interchange on I-75 between those two Florida cities was all where the freeway crossed over each time.

Not to burst any bubbles, but there are two other interchanges along I-75 between Tampa and Naples where the mainline travels under its intersecting road: Exit 250 (Gibsonton Drive) and Exit 105 (Golden Gate Parkway). And out of those three, Exit 250 was the only exit of this style that was built when the freeway was originally built.

[mhh]

In most cases the freeway will carry much more traffic than the intersecting road. When topography permits, it makes sense to keep the freeway level so the majority of the traffic will have less hill climbing and better forward visibility at high speeds. When heavy trucks lose speed going up slopes, it can create a hazard for cars behind them.

Makes sense. But it doesn't explain roadman65's observation that the interstates cross most of the intersecting roadways when there is an exit involved. Why not the other way around?

Interestingly, heading north on I-75 into Georgia, a great many of the interchanges north of the border cross the secondary roadway OVER the interstate (assuming no co-located railroad - i.e., Exit #16).

I'm not familiar with the Florida freeways so I have no explanation. In Michigan, nearly all intersecting roads go over freeways, with the freeways remaining level, except where topography is an issue.

[jwolfer]

In most cases the freeway will carry much more traffic than the intersecting road. When topography permits, it makes sense to keep the freeway level so the majority of the traffic will have less hill climbing and better forward visibility at high speeds. When heavy trucks lose speed going up slopes, it can create a hazard for cars behind them.

Makes sense. But it doesn't explain roadman65's observation that the interstates cross most of the intersecting roadways when there is an exit involved. Why not the other way around?

Interestingly, heading north on I-75 into Georgia, a great many of the interchanges north of the border cross the secondary roadway OVER the interstate (assuming no co-located railroad - i.e., Exit #16).

I'm not familiar with the Florida freeways so I have no explanation. In Michigan, nearly all intersecting roads go over freeways, with the freeways remaining level, except where topography is an issue.

Different from most other states for sure. Driving from jacksonville to Orlando on i95 and i4 I think the only original exit that had the interchange pass over the interstate was SR 436.

I work off SR 436 and coming up on i4. I missed getting in i4 a couple time because I am so used to seeing the interstate passing over the road

[NE2]

Driving from jacksonville to Orlando on i95 and i4 I think the only original exit that had the interchange pass over the interstate was SR 436.

Most Volusia County interchanges on I-4 are Interstate under; the only one that isn't is CR 4162, which had a railroad next to it. Then there's Anderson, SR 435, US 192, and US 27 in the Orlando area. It's probably mostly due to terrain; west Volusia is a bit hilly for Florida, as is Polk, where there are a lot more I-4 unders. But I-95 goes through pretty flat areas, and so does I-75 south of Ocala (with some I-75 unders in the hills, such as CR 41).

My guess is that they first determine the general grade for the freeway, including cuts and fills, then see whether a freeway over or under would require less work.

[jakeroot]

My guess is that they first determine the general grade for the freeway, including cuts and fills, then see whether a freeway over or under would require less work.

Absolutely. Go to any hilly area, like Seattle, and count the number of overpasses versus underpasses. I'd imagine that there's about an even number of both.

[jdb1234]

Then for I-75 the Laurel- Nokomis interchange near Venice is the only interchange south of Tampa and North of Naples where the road crosses over I-75 and that one was added sometime in the early 90's, so it would mean that every interchange on I-75 between those two Florida cities was all where the freeway crossed over each time.

Not to burst any bubbles, but there are two other interchanges along I-75 between Tampa and Naples where the mainline travels under its intersecting road: Exit 250 (Gibsonton Drive) and Exit 105 (Golden Gate Parkway). And out of those three, Exit 250 was the only exit of this style that was built when the freeway was originally built.

And in the Tampa area I-75 travels under FL 574 @ Exit 260. 

[Fred Defender]

Then for I-75 the Laurel- Nokomis interchange near Venice is the only interchange south of Tampa and North of Naples where the road crosses over I-75 and that one was added sometime in the early 90's, so it would mean that every interchange on I-75 between those two Florida cities was all where the freeway crossed over each time.

Not to burst any bubbles, but there are two other interchanges along I-75 between Tampa and Naples where the mainline travels under its intersecting road: Exit 250 (Gibsonton Drive) and Exit 105 (Golden Gate Parkway). And out of those three, Exit 250 was the only exit of this style that was built when the freeway was originally built.

And in the Tampa area I-75 travels under FL 574 @ Exit 260.

And, just south of SR780 in Sarasota, I-75 crosses over Palmer Boulevard (no exit).

[FLRoads]

Then for I-75 the Laurel- Nokomis interchange near Venice is the only interchange south of Tampa and North of Naples where the road crosses over I-75 and that one was added sometime in the early 90's, so it would mean that every interchange on I-75 between those two Florida cities was all where the freeway crossed over each time.

Not to burst any bubbles, but there are two other interchanges along I-75 between Tampa and Naples where the mainline travels under its intersecting road: Exit 250 (Gibsonton Drive) and Exit 105 (Golden Gate Parkway). And out of those three, Exit 250 was the only exit of this style that was built when the freeway was originally built.

And in the Tampa area I-75 travels under FL 574 @ Exit 260.

Not sure how I forgot about that one! I used to use that exit to get to a former job! lol

[GCrites]

Excellent thread idea.

I've been wondering about this since the early '90s.

[jcn]

What's funny is if you're on I-95 from Philadelphia to the Capital Beltway most of the interchanges cross over I-95.  Not counting viaducts, the only interchanges I know of off that stretch that go under I-95 are Southbound I-476 (Exit 7), US 322 (Exit 4), and PA 452 (Exit 2) in PA, Marsh Rd (Exit 9) and DE 1/7 (Exit 4) in Delaware, and MD 279 (Exit 109), I-695 both times (Exits 64 & 49), US 40 (Exit 61), Dundalk Ave (Exit 58), and MD 32 (Exit 38)* in Maryland. 

*Note that MD 32 actually crosses under northbound 95, but crosses over southbound 95.

Once I-95 becomes concurrent with the Capital Beltway, most of the interchanges go under the highway if I'm not mistaken.

[Mapmikey]

A couple other theories about why Florida could have done this in flat terrain, both of which could be completely incorrect...

A diamond interchange with the interstate going over it should take up a smaller footprint which might have been important to them.

It is easier (and sooner) to see cars coming along the on-ramps from an interstate bridge as opposed to when the on-ramps come from an elevated roadway.