What is the speed of Halley's comet?

The comet has a changing velocity, from around 1 km sec at aphelion to 100 km/sec or more when it is closest to the Sun. The speed estimated as it passed Earth's orbit in 1910 was 70 km/sec (254,016 km/h or 157,838 mph).

Like everything else in space, Halley's Comet follows an elliptical orbit. When it is closest to the Sun, it is moving fastest, and when farthest away, it is moving quite slowly. Right now, Halley's Comet is out beyond the orbit of Neptune, moving slowly and slowing down even more as it climbs away from the Sun. In about 10 years, it will reach aphelion, at which time it will be almost completely stopped relative to its distance from the Sun, and then it will begin the long fall into the inner solar system.