I understand that high speed turnoff is for the plane to exit the runway asap. What is its design specification and how fast can a plane use highspeed turnoff? Assuming only A320,737 and larger.
Please be careful applying a blanket figure during high speed turnoff. There are many variables which you should consider. These are:
• Exact angle of the taxiway(you're turning onto): If it's a very shallow angle off the runway and therefore does not require much turning, high-speed turnoffs are easier and manageable, and vice versa.
• Rate of deceleration
• Side load limitations on the CRJ
• Tolerance of the nose gear
• Traffic situation on taxiway
Generally speaking you need both sets of eyes outside, especially if you are joining or crossing another Taxi Way.
According to AC 150/5300-13A, section 409:
b. High-speed exit taxiways. A specific case of an acute angle runway exit taxiway that forms a 30-degree angle with the runway centerline is commonly referred to as a “highspeed” exit taxiway. The purpose of a high speed exit is to enhance airport capacity.
Since the parameters of high-speed taxiway design is the angle at which the taxiway intersects the runway, and does not take into account the aircraft speed, then the answer will be different for every aircraft.
From the Jeppesen glossary, page 14 of this PDF:
HIGH SPEED TAXIWAY / TURNOFF (HST) — A long radius taxiway designed and provided with lighting or marking to define the path of an aircraft, traveling at high speed (up to 60KT), from therunway center to a point on the center of a taxiway. Also referred to as long radius exit or turnoff taxiway. The high speed taxiway is designed to expedite aircraft turning off the runway after landing, thus reducing runway occupancy time.