The start was too great

From "The hound of the Baskervilles" by A. C. Doyle:

At that instant I was aware of a bushy black beard and a pair of piercing eyes turned upon us through the side window of the cab. Instantly the trapdoor at the top flew up, something was screamed to the driver, and the cab flew madly off down Regent Street. Holmes looked eagerly round for another, but no empty one was in sight. Then he dashed in wild pursuit amid the stream of the traffic, but the start was too great, and already the cab was out of sight.

What does "start" mean here?

I believe "start" is referring to "and the cab flew madly off down Regent Street."

Scott

Quote:

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Originally Posted by Inego

From "The hound of the Baskervilles" by A. C. Doyle:

At that instant I was aware of a bushy black beard and a pair of piercing eyes turned upon us through the side window of the cab. Instantly the trapdoor at the top flew up, something was screamed to the driver, and the cab flew madly off down Regent Street. Holmes looked eagerly round for another, but no empty one was in sight. Then he dashed in wild pursuit amid the stream of the traffic, but the start was too great, and already the cab was out of sight.

What does "start" mean here?

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The start means the head start or lead that the carriage had when SH started running after it; this distance was so great that SH couldn't catch the carriage.

Thank you!