Agreed, but they operate three tunnels of a fair length, which are part of a major international traffic route (Euroroute E22), and are regarded as one of the most modern operations of road tunnels in the UK. If you were to consider building long road tunnels, I'd suggest having a word with NMWTRA to benefit from their expertise.
(I've had the priviledge of having a site visit to their control centre and one of their tunnels during a maintenance closure. There's a heck of a lot going on in terms of lighting, ventilation, vehicle detection, traffic monitoring, lane control, fire risk management, etc. that the average driver doesn't notice as they whip through.)
Would I be right in assuming that these are straight tunnels with no junctions, if that's the case they would still be far simpler to operate than something with a junction on it.
Even if you could find an exit portal location within a city, what then happens to those vehicles? Unless it directly links to a car park those cars are just going to clutter up the city, either by driving around or needing somewhere to park (or most likely both).
If you're going to the expense of building a multi lane tunnel you might be better off building a logistics hub at one end and have a system similar to those the airports use for dealing with baggage to get deliveries in and waste out.
For those expecting deliveries they could be delivered to the hub and get a notification that they have a parcel, they could then schedule a delivery slot at time which suits them to a hub within (say) 100m of their address. With a large enough system shops could deliver items directly to individual building, especially for blocks of flats (for example you could get your supermarket shopping without the supermarket needing to operate vans within the city, but also independent shops could also offer a delivery service when they otherwise couldn't).
Even large items could be delivered (although you may want to have a more limited number of hubs which could deal with those items beyond a certain weight), likewise waste could be taken away (almost) straight away, meaning no need to store large bins and the problems that causes.
It would have a big impact on public transport use too, as the need to move large items by car (even if that's rarely) would be significant reduced.
You could even have a car hire hub on the system, so people could send their luggage to it to then pick up a hire car to go somewhere with limited public transport. This would also reduce range anxiety when using EV's, as the total distance travelled would be smaller.
Of course, by doing something like this it would mean disposing if a lot of jobs (postal services, fast food deliver, etc.), however given the working aged population is likely to continue shrinking (at least as a percentage of population) arguably that's going to free staff up to do other work. However depending on how close the hubs are too people there could still be some demand for hub to door delivery, so that may not remove all the delivery jobs (especially if more deliveries are made due to it being easier).
It would however create other jobs, for example, maintenance staff. Likewise, it could mean more opportunities for businesses, meaning that they require staff for their core business (for example, Dominos may require more people to make the food, and whilst this may not replace all the staff lost from their deliveries, it's likely to reduce the impact - it could also change the pricing, in that you don't need to price to your delivery capacity, just look at the better offers you can get by collecting or at certain times).
Postal services could send a pack of letters/parcels to a location for delivery, in doing so there would be no need for vans. As even if the delivery was from the local hub to your front door, the number of items such a delivery worker needed to move would be quite small at any given time, and so they could either carry them or push them on a trolley (especially if there was a larger parcel) the short distances required.
All movements are likely to incur a charge, however the staff time savings are likely to be significant and so the cost would most likely be offset. For example, whilst sending a single letter would be more expensive than posting it, sending a small parcel (which could contain a hundred letters) would be cheaper. You could, (once you've got a delivery to the hub) go and get it or pay a bit extra for a to your door service.
It wouldn't work in places with limited population density (although it should be noted that it's much more likely to work in the UK than the US, as even small towns here can have the population densities which put them into the top 10 most dense cities in the US, as anywhere with a population density of over 3,200/km2 would meet that requirement (somewhere like Alton in Hampshire is like that), somewhere like Manchester is 4 times that, with it likely that areas of the city are even higher still.
Of course, such a system is far too disruptive to actually happen, even if it was of a cost that was comparable to other projects which wouldn't have the same benefits.