Question

If the flow ratios for the lane groups NBLT, SBLT, NB, SB, EB, and WB are 0.19, 0.16, 0.30, 0.28,0.30, and 0.26, respectively, do we need an overlap phase, yes or no?

What is “average speed” we use in the relationship where flow is density times speed?

a. time mean speed

b. space mean speed

What types of locomotive works best for urban transit system?

a. diesel-locmotive

b. diesel-electric locomotives

c. electric locomotives

d. steam locomotives

Answer 1

i)

The sum of flow ratios of all phases must be unity (1).

If we provide free left turn for the Northbound left turn (NBLT) and Southbound Left turn (SBLT) there is no requirement for phase overlap. But if we do not provide free left turn all the traffic flows must be considered.

For the given lane groups, the sum of flow ratios =

=0.19+0.16+0.3+0.28+0.3+0.26

= 1.49

So we are getting sum of flow ratios more than one.

So we must have an overlapped phase for the given flow ratios.

ii)

The fundamental relation between flow(q) , speed(v) and density(k):

q=k x v

Here the speed v is space mean speed.

iii)

Steam locomotive:

A steam locomotive is a locomotive whose primary power source is a steam engine. The most common form of steam locomotive also contains a boiler to generate the steam used by the engine. By the end of the 20th century, almost the only steam power remaining in regular use around the world was on heritage railways.

Diesel locomotives:

Diesel locomotives are powered by diesel engines. In the early days of Diesel propulsion development, various transmission systems were employed with varying degrees of success, with electric transmission proving to be the most popular.

Diesel – Electric locomotives:

In a diesel–electric locomotive, the diesel engine drives either an electrical DC generator (generally, less than 3,000 horsepower (2,200 kW) net for traction), or an electrical AC alternator-rectifier (generally 3,000 horsepower (2,200 kW) net or more for traction), the output of which provides power to the traction motors that drive the locomotive. There is no mechanical connection between the diesel engine and the wheels. The vast majority of diesel locomotives today are diesel-electric.

Electric locomotives:

An electric locomotive is a locomotive powered only by electricity. Advances in electrical grid infrastructure and electric engine manufacture enabled trains to adopt electrical power as one of the most reliable sources of propulsion. Today electrical trains can be found everywhere, from city transit trains, subways, trams, to high speed rapid transit trains.

So for the urban transport, Electric locomotives are best in terms of providing high speeds.