And even if the land is public, who owns the road bed? If its a county road, you'll likely need county permission. State road? You ain't getting permission. Town road? Maybe?
There's a reason "road trapping" isn't done in WI any more.

And if you are talking about driveway culverts, be sure to check where the ROW truly is. "Roads" are a heck of a lot wider than the pavement.

Beav has done the work for you. Here in NE we had multiple problems with every video or book saying to trap road bridges/culvert, so much so that a NFH group went down to the Legislature to testify in '87. One legislator was in a bind as it was his constituent (a paid state lobbyist) who had their dog killed in a 220 size BG (already totally illegal then) and this elected guy wanted to outlaw ALL trapping along side ROW's. We had the state employees union against us as they thought workers were in danger and a whole bunch of "bleeding hearts" (including PETA) against us. I gave testimony and the elected senator (along with everyone on their side) choked. Committee adjourned until the next day and the senator (Jerome Warner from Waverly) hotfooted to the Attorney General's office to to find some way to bail him out. Long story short they dug up the LAW's wording (before WS's above statement) that the LANDOWNER (title holder) is the only one with the right to grant permission to TRAP on their land (covered under the trespass clause). We (NFH) compromised on that and left the chamber. So the state or county or township or individuals who actually OWN the ROW must grant permission to trap there. Majority of county roads here are owned by the legal description of the tract, state roads by DOT and very very few by the county - your GIS maps will be able to tell who is the deed holder of that property. That ruling in committee, opened more NE Game and Parks regulations (not law) to constitutionality but that's another topic. So w/o looking up and interpreting your Trespass laws I think Beav's advice is sound. AND a side note,,,,,,,,,,,,,,,,, for all those pseudo trappers that advertise their "skill and secrets" making sets along bridge walls and at road culverts,,,,,,,,,,,,,,,,, take that away from them and see how much and how good of a fur harvester they are. The majority of states don't have legal access to those spots as the very few that do limit a person's wildlife knowledge from my view. This is from the guy who was setting 330's in culverts totally legal in '72 and has a "few" years experience. Off my soap box.................. the mike

Dry culverts have been productive for me for bobcats and gray fox (also with bodygrips for racoons and skunks).

This culvert has produced quite a few cats thru the years.

I've also had great success in them for beaver and muskrats (though it's been a few years since I trapped them).

They can be good for the sneaking trap thieves. But they can be very productive.

It kind of sucks having to get permission but after the first time, they know you and you get welcomed back. I show the property owners what a DP looks like and tell them we have a calendar day check time. If anyone asks, I’ll even snap a DP on my finger to show them it's a holding device. Many have used them with varying degrees of success. Then I tell them I use a release pole in case a cat gets caught. It happens from time to time. I think this last season I got turned down twice. Most farmers WANT to get rid of the coon, skunks and possums.

Years ago I was able to run 200 traps setting every bit of water I crossed. Now it's about impossible with the Wisconsin trapping regulations.

One of my biggest problems is finding a landowner to contact. Everything is a corporation or LLC. I’ve cold called plenty, but rarely get yes off of those

I have had more traps messed with on private property than on ditches and crown land-go figure

not being allowed to trap culverts and waterways that cross roads is really crappy-feel bad for you Wisconsin guys and anywhere else it isn't allowed

I believe Most States have the rules, regs and actual laws regarding landowners Rights of Use (and restrictions) on their ROW property. And if you want to play law clerk, a lot of those states where you CAN harvest fur on a ROW without permission, it is not legal. It gets over looked or not researched enough to warrant an "attorney's opinion" (prior to court). I was trapping roadsides in MI in the mid 70's when I went to MSU and was not aware that it needed landowner permission then. Same goes for "spring loaded snares" (Senneker vs. Ram) in Iowa or other states. It will take one knowledgeable with the mechanics of the device and one familiar with the law to sort usages out. As I stated above, Beav has done the work for you on ROW in your state and if a road goes through a public wildlife area the "owner" (DNR, State, County or Township etc.) has those rights to grant usage. Now back to the question,,,,,,, Yes a few of us "old timers" have run auto lines for rats and mink specifically in the culverts. Unfortunately, winter with ice, blowing and drifting snows limit sets to the deeper water ones. Baited and non-baited BG's and tunnel traps worked for me. I quit after 4-5 years of it and waited for the spring season (open water) where it was easier and could anticipate more animal movement. February was and still is Mink Movement Month for me in every state I trapped. My experience. ..........the mike

[ yup iowa rocks longlineing]