Rental car Frankfurt - Alsace & Black Forest – cross-border restrictions a real problem?

I'm not qualified to address the permits/environmental rules.

Have you dropped the Middle Rhine Valley from your plans? It's not mentioned.

Picking up at FRA airport and driving straight to the BF or Strasbourg is a lengthy and inadvisable drive immediately after a night-time transatlantic flight across several time zones. If that's the current plan, I would probably pick up a car for the Alsace as you suggested, but only after visiting Strasbourg for however many days you have planned there; rather than drive to Strasbourg from FRA, I'd opt for the train ride on day #1, enjoy Strasbourg, then pick up the car there for the remainder of your stay in France. Doing it this way makes day #1 safer and could make for a less expensive rental; a car isn't needed just to visit Strasbourg.

The details of your trip in Germany aren't clear, but it could easily make sense to drop the car back in Strasbourg and hop across the border by train to Gengenbach or wherever you are staying in the Black Forest (short train ride, cheap day pass for this trip is available.) Offenburg, just outside Gengenbach, is a railway hub AND a good place to pick up your car for the rest of your time in Germany.

Gengenbach is one of the "KONUS" towns, meaning that you receive a Guest Ticket for free train trips during your stay; your trip will be by car, but you might also enjoy the scenic train ride between Gengenbach and the higher-elevation Black Forest towns of Triberg, Villingen, Donaueschingen that line on the Black Forest Railway:

https://upload.wikimedia.org/wikipedia/commons/4/4d/Verlaufskarte_Schwarzwaldbahn_%28Baden%29.png

Just left the rental car agency know that you’ll be driving to France and they’ll make sure that you get the sticker on your car. Many countries are like that. For example if you were to drive into Austria you would need one as well. But it’s not a big issue.

I did a very similar journey this past summer without any issues. Picked the car up at Frankfort Airport, drove to Colmar and nearby towns then back to Germany with stops in Freiburg and Kunzelsau before returning to Frankfort. You can check with the rental car agency to confirm but you should be okay. There is, of course, a fee for taking the car across borders - you should check this with your rental agency.

The only issue we had was a parking fine in Freiburg. We carefully checked the signs and with someone in the area and thought we were good but apparently we weren't. We asked our German friends about it and they said this happens to them from time to time - apparently all the parking rules are not completely clear and there is nothing you can really do about it if you get a ticket.

When we visited in 2023 Strasbourg was the only town in the Alsace area where an environmental/low emissions sticker was needed. Since our Germany rented car didn’t have the French sticker we stayed in Colmar and took the train to Strasboug. If staying in Strasbourg consider contacting your lodging to see if it’s possible to drive to it, then park it for the duration of your stay in Strasbourg.

Crossing borders generally isn’t an issue, but inform the rental company when picking up the vehicle that you will be crossing. Although I’ve never been charged a fee, some companies levy a fee (about €50) for taking the vehicle into other countries. If you don’t inform the rental company and something happens to the vehicle there could be insurance ramifications for you.

Since there are many more towns in Germany requiring an environmental sticker than in the Alsace region rent in Germany. Without the vehicle registration/license late number it would be impossible to get a French environmental sticker. Even with it, getting one in time for the trip would be nearly impossible. The environmental sticker is different from the vignettes needed to drive on the highways in Austria or Switzerland.

On our trip we picked up and dropped off the rental in Frankfurt then headed to the Black Forest area, then the Alsace area of France. We then went up to Belgium, over to Luxembourg, and back into Germany where we followed the Mosel and Rhine rivers.

After the long flight we spent the first night in Bensheim to get over jet lag. It’s about a 30 minutes drive south of Frankfurt airport. Have some Euros with you since many places in Germany still only accept cash. In Bensheim, both the cafe and restaurant we went to only accepted cash, so it was a good thing we had some on hand. I got more Euros from an ATM prior to departing.

To check which places require an environmental sticker, I use the Green-Zones app.

Crossing the border is not a problem.

If your trip only includes Alsace and the Black Forest, Strasbourg is the only place where you'll run into a sticker issue. However, a rental company based in Frankfurt won't provide a Crit'Air sticker for Strasbourg; even without an emisions sticker requirement, Strasbourg is not the best place to stay with a car.

Day trip to Strasbourg? Park in Kehl or Selestat and take the train in. Kehl is closer and has free parking (still?). Two day is good, if you include museums.

Yes, cash is still good and preferable in many locations.

I'd day trip into Basel once or twice.

As most are indicating, the biggest issue has to do with Environmental requirements and "passes" for driving on certain roads, or Vignettes.

A number of German cities require an emissions sticker, but one would assume a car rented n Germany would have that, and being a newer car, meet requirements for restricted areas.

Strasbourg is the only French city of concern on your route, do not assume the rental has the sticker, you can ask, but to be safe, you could either day-trip from one of the other stops, or drive to Kehl, Germany(Just across the river from Strasbourg); park, and head into Strasbourg by train. You can even leave the car overnight at the train station, cost a few euro per day.

You might look into the requirements for the Swiss Vignette. You may not be straying into Switzerland, but in case...

In a prior post you indicated that you would spend two or three days sight seeing around Frankfurt before renting a car. That, in my opinion, is a very wise thing to do. You will be tired, sleepy, jet lagged, and on strange turf. Driving in that condition is not the way to start a trip. Even a minor fender bender at the beginning can be a real downer for the rest of the trip. Personally, I shouldn't be allowed to handle sharp instruments after an overnight flight.

There are many places just an hour or two by train that you can visit while you become acclimated.

Don't mean to sound like Grumpy Gertha, just offering food for thought.

A German rental car will not have the French Crit d'Air. Strasbourg require this to drive into the city, and depending on the number within specific areas (such as the old town). The Crit d'Air is not like a Vignette such as Austria or Switzerland require. It is a sticker specific to the VIN of the vehicle you are driving. You must apply for this, and it takes time to arrive. I applied for one for my new car two weeks ago and am still awaiting the decal.

You can pass over the border between France and Germany without a Crit d'Air. But there are patrols on the German borders and they may stop you on the return. Be sure to have your paperwork and passports with you.

Parking in Strasbourg is expensive, averaging 40+ euro/day.