how fast does a comercial aircraft (e.g. Boeing 737-800) travel on
long (10,000 feet) prallel taxiway?

Dear runwayreporter-ga,

I have referred to a number of different sources to compile this
answer. Once a plane lands, its speed is reduced to taxiing speed; for
take-off, taxiing speed is increased to take-off speed.

For the Boeing 737-800, these are the relevant landing and take-off speeds.

Take-off speed (full):290 km/h
Landing speed: 260 km/h
http://www.airberlin.com/site/aboutflotte.php?LANG=eng

Take-off speed 290 km/h
Landing speed 205-283 km/h 
http://www1.aua.com/en/lauda/airplains/b737800.asp


As for taxiing speeds, these vary at airports and is often left to the
discretion of the pilot and where they are on the airport runway. This
is information for Heathrow (London) airport.

10000 feet is 3048 metres.

The runways at Heathrow (London) are 3902m and 3658m in length.
http://www.ukaccs.info/profiles.htm

During the Heathrow Terminal 5 enquiry, air traffic was averaged as follows:

?Taxiing speed: 27.5khp 15 knots?
http://www.dft.gov.uk/stellent/groups/dft_aviation/documents/page/dft_aviation_503332.pdf

For Stansted (another UK airport), ?a constant taxiing speed of 15
knots is assumed throughout, although in practice aircraft often taxi
faster than this along straight runs and slower around bends.?
http://future.stanstedairport.com/main/assets/pdf/generation1/Environmental-Statement-Vol-8-Ground-Noise.pdf


I hope this answers your question. If it does not, or the answer is
unclear, then please ask for clarification of this research before
rating the answer. I shall respond to the clarification request as
soon as I receive it.
Thank you
answerfinder

There is an airspeed, S_a, such that the lift component of forces
acting on the aircraft equals the craft's weight. At this point the
coefficient of friction between the wheels & the runway surface =
zero, and the plane cannot steer. For speeds > S_a, the lift
acceleration exceeds gravitational acceleration, and the ship becomes
airborne. By this reasoning I assert that...

   ...runway taxi speed < S_a. 

I'M GLAD TO BE OF HELP! NO THANKS NEEDED! ;)