Here's something else to remember; Washington's heat and humidity...yes it will be there.

Not next week.

"the taxi hire is for a driving tour and not a car service to wait while you get out and visit."

Hmmm. I would expect that if I hired a taxi for an hour it would be for me to decide whether he spends that time driving me around or sitting still while I walk around the Jefferson Memorial. Also, the cabbie might prefer to wait around as that burns a lot less fuel than driving does.

Oops, sent too soon -- I guess the thing to do if you are interested in a taxi by the hour is to negotiate such things with the driver. I wonder if some drivers are just not interested in taking hourly fares, and if the requirement that they take any passenger anywhere within the city means they must accept an hourly fare.

Here is a tour guide I just found on TA that gets excellent recommendations, would pick u up at airport, etc. and tailor your trip to your needs. http://www.toursofdc.com/

Even though it is expensive I think it would be worth having someone such as this company tailor your tour to your sister's needs. DC has a tremendous amount of walking involved. You could pick what you want to see for the time you have the guide.

I have a friend that did the trolley tour this past fall and it took them to Arlington Cemetery. We were at the cemetery a couple of years ago and several tour busses were there. You can also book a tour at the visitor's center. The downside of the trolley tours is if it is crowded in DC then you have to wait for a pickup and the trolley could be full by the time it gets to your stop so you have to wait for the next one to come along. I would opt for taxi or private tour if it were me, given your sister's health.

Depending upon her mobility, perhaps the Segway tour might work also.

Good luck, hope you enjoy DC. My daughter, son-in-law and 2 grandsons are flying there as I write this. Hotels are sold out this week as it's spring break in the northeast. Hopefully, it will be less busy next week.

I have also just discovered "pedi-cabs"..$75 for the hour and they take you anywhere along the mall and monuments.

I found the DC taxi fare web page confusing so I wrote asking "When I rent the taxi for $25/hour, is the meter running or not?"

A reply email from the Public Information Officer for the DC Taxicab Commission said:
"The meter should not run when a passenger engages the services of a taxi for a set amount of time."

So, the hourly fare is instead of the meter fare, not an "extra" on top of the meter fare. Quite a bargain, it seems to me.