Given a travel related situation, and given a specific question about the situation, summarize the question into a title

[Q]: We are going to spend 2 days in London in mid-December and we wonder if we should buy the London Pass which is 46.00 per day per adult. It is not the first time we have used this kind of pass and have always been satisfied with it in the past. However, this one seems pretty expensive to me. Would I save much money by paying the 184.00 for the two days in London?

[A]: Is the London Pass worth the price?

[Q]: Here's my situation: I'm a UK citizen. I have an H-1B visa to work in the US as of 1 August. I also have a valid ESTA.

I would like to go to the US in July for a holiday, immediately prior to beginning my work. The holiday would be at the other end of the country from my work.

I can't enter with the H-1B as I can only enter the US on that visa 10 days prior to starting work.

Specific question: Would it be possible to visit the US in early July on the VWP, visit Canada/Mexico for a few days in late July, and re-enter the US with my H-1B visa?

General question: Is it possible to visit the US on the VWP, leave briefly, and re-enter on a different status (e.g. H, F, J, K, etc), without ever returning to one's home country?

I have posted this in Travel rather than Expatriates because, although in my specific case I have an H-1B visa, my question is more generally about VWP and travel, and I believe that it is applicable to travellers with non-immigrant visas.

There's a similar question here, although that's about going to the US and before having the H-1B visa.

[A]: Can I visit the USA as a VWP tourist immediately prior to entry on non-tourist visa?

[Q]: When driving on a US interstate highway, how will I know if an upcoming exit ramp will be followed by an entrance ramp to re-enter the highway after exiting? (e.g. if I need a gas station or food break)

In rural stretches re-entry is almost always possiblebut not always. In cities, especially where various freeways meet, I feel like re-entry is much less common. But how to know in advance without trial-and-error?

(When I started driving I had erroneously thought that if the exit says "Exit only" in yellow, there would be no return entrance, but I now believe this refers to the specific lane being forced to exit, which is really nothing to do with ability to re-enter after exiting.)

[A]:
How can I know if a U.S. interstate exit will have a return entrance ramp?