Comparison of interchanges

Comparison is made for interchanges which allow higher speeds also on the left directional ramps and thus ensure greater traffic capacity:

• ITL Interchange
• Stack Interchange
• Turbine
• Pinavia

There are also other types of interchanges. However, at these interchanges, a crucial speed reduction is required when turning to the left. These interchanges are: Cloverleaf, Contraflow Left, Diverging Windmill ... Due to the low cost of construction, the Cloverleaf is included in the comparison. However, for the same area of the entire interchange as ITL Interchange, the Cloverleaf has a much lower speed limit for turning to the left. The Cloverleaf also has conflicting points, while other interchanges do not.
Comparison is made for interchanges with horizontal radii for the left directional ramp R = 250 m and R = 550 m. These radii allow driving at a speed of 80 km/h and 100 km/h. In case of the Cloverleaf on the same area, horizontal radii are R = 100 m and R = 225 m for turning to the left.

Parameters:

• Radius of the horizontal circular curve for left directional ramps R = 250 m / R = 550 m (Cloverleaf R = 100 m / 225 m)
• Maximum transverse inclination 7%
• Vertical rounding with a convex radius of 4000 m and a concave radius of 3000 m (at horizontal R = 250 m) and with a convex radius of 9000 m and a concave radius of 6000 m (at a horizontal R = 550 m)
• Maximum longitudinal inclination 6%
• Altitude difference between individual levels 6 m
• Permissible speeds 80 km/h (R = 250 m) and 100 km/h (R = 550 m)

Results of comparison

1. Area

R = 250 m (Cloverleaf R = 100 m)

The smallest area is needed for the Stack Interchange, 18.5 ha. On the other hand, the largest area is needed for the Turbine. This interchange extends at 58 ha. The area for other interchanges is 33 ha.

R = 550 m (Cloverleaf R = 225 m)

With this radius, the difference in the area of the interchanges is even more pronounced. Stack Interchange has an area of 79 ha and Turbine of 260 ha. The remaining interchanges need an area of 142 ha.

Area

2. Lengths of ramps and overpasses

Stack Interchange, Turbine and Cloverleaf have a completely straight lines when driving through. ITL Interchange has a slightly longer distance due to the separation of carriageways. Pinavia has an even longer distance because lanes run along the circle.

Construction for right directional ramps is similar in all cases. ITL Interchange and Stack Intercgange have the shortest lenght of ramps. The Cloverleaf and Pinavia have an approximately double length, and Turbine, due to its size, has about a triple length according to the most favorable variants.

However, construction for left directional ramps totally differs. There are the greatest differences between compared interchanges. Ramps mostly lead over the overpasses. ITL Interchange has an extremely short length of ramps. A little longer distance is in the Cloverleaf, but due to the small radius, there is a lower speed limit. The distance is greater by factor 2 on Stack Interchange and more than by factor 3 on Pinavia and Turbine.

Cloverleaf has the shortest length of overpasses. However, it has lower speed limits for turning to the left and some conflic points. At other compared interchanges, ITL Interchange has the shortest length of overpasses. The distance of overpasses is greater approximately by factor 2.5 on Stack Interchange and Turbine. Pinavia has by far the highest lenght of overpasses. Compared with ITL Interchange, the factor is more than 5.

More technical data for each interchange and comparison with horizontal radiuses R = 250 m and R = 550 m:

Specification R=250m		Specification R=550m

Traffic Capacity

Capacity estimation of ITL interchange is made and comparison between some of the most common used highway interchanges.
Traffic simulation techniques has been used. Delay analysis of ITL interchange has been done by microsimulation software PTV VISSIM.

Parameters:

• The comparison is focused on Delay, Average Speed and Distance Travelled.
• Three different load scenarios (2500 veh/h, 3500 veh/h and 4500 veh/h).
• Composition used: 90% Cars and 10% HGV.
• O/D Matrix

		0	0,33	0,33	0,33
	ρ1 =	0,33	0	0,33	0,33
		0,33	0,33	0	0,33
		0,33	0,33	0,33	0



• Geometric parameters: radius of the horizontal circular curve R = 250 m, maximum longitudinal inclination 7%, permissible speeds 80 km/h

Graphical representation of results:

Comparison of Average Delay

Comparison of Average Speed

Conclusions-Performance Analysis:

• For higher traffic volumes (4500 veh/h), the ITL Interchange has better performance and offers much lower delays.
• For lover traffic volumes (2500 veh/h), the ITL Interchange has almost the same Average Delay (3,6 s/veh) than other geometry.
• Average Speed and Total Distance Travelled are much higher for ITL Interchange.

Summary

The characteristics of interchanges which stand out with their positive or negative characteristics from other intersections:

Advantages

Disadvantages