Types of Road Patterns in Highway Engineering

In urban areas, achieving a smooth traffic flow is a challenging procedure. While planning a road system for urban areas, special care and precaution are to be taken to provide accident-free traffic flow. 

The main principle of a road system is to increase the response time of average and emergency vehicles, like ambulances, fire engines, etc to reach the final destination. A road pattern suitable for a particular area would not be suitable for another area. 

This article explores the various road patterns adopted for planning roads in early-developed cities or renovating the existing roads.

Types of Road Patterns

The major types of road patterns recommended in highway engineering for highway construction are:

1. Minimum Travel Distance Pattern
2. Rectangular or Block Road Pattern
3. Radial or Star and Grid Pattern
4. Radial or Star and Circular Pattern
5. Radial Star and Block Pattern
6. Hexagonal Pattern

1. Minimum Travel Distance Pattern

A minimum travel distance pattern is defined as a route that is the shortest and most efficient route or path a person or vehicle takes to reach a destination. In this system, the road is divided into nodal points around the central portion thus forming sectors as shown in Figure 2 below. Each sector is divided again in such a way that the distance from each of the nodal centers to the central place is minimal.

Fig.2. Minimum Travel Distance Road Pattern

A city with such a road pattern will have a sector center, sub-urban centre, and neighborhood centre by the roads which require a minimum distance to connect to the city centre. 

The minimum travel pattern for a city can be determined using various methods like network analysis, routing algorithms, and optimization techniques. It is also influenced by the traffic in the area, road conditions, and population. The finally obtained road pattern will be routes that minimize the distance or the time taken for travel which in turn helps to provide a cost-effective and efficient transportation planning and analysis solution. 

2. Rectangular or Block Road Pattern

In this type, the whole area is divided into rectangles or blocks such that the streets intersect at right angles as shown in Figure 3. This will have main roads that pass through the center of the area, which is sufficiently wide and derive branch roads that may be comparatively less wide or narrow. The main road finally will be a direct way out of the city. 

Fig.3 Rectangular or Block Road Pattern

Advantages

• The construction and maintenance of such types of road patterns are easier compared to other patterns.
• The rectangular plots formed can be further divided for future construction of buildings placed back to back, having front-facing roads.
• This type has a good aesthetic view and the road geometry is easy to understand.

Limitations

• Not convenient from a traffic point of view, because at intersections the vehicles come face to face causing traffic issues.
• This type of road pattern is mostly formed far away from streets, hence it takes time to reach the center of the area or the city. 

3. Radial or Star and Block Pattern

As the name says, the entire area is divided into a network of roads radiating from the central business outwardly. In between the radiating main roads, the built-up area as shown in Figure 4 may be planned with a rectangular block pattern. Hence, it is a combination of radial and block patterns.

It is a pattern where radial main roads exist and in between these radial roads, a block pattern is formed. Here, ring roads or concentric roads like the star and circular pattern do not exist. 

Fig.4. Radial Star and Block Pattern

Advantages

• Minimizes congestion at the main bottleneck location.
• Blocks traffic from entering local routes toward the event venue, prioritizing the flow of outgoing traffic.
• In case of the road closure, vehicles can divert to alternative routes.
• Vehicles encounter fewer instances of facing each other compared to a blocked pattern.

Limitations

• Demonstrates enhanced effectiveness when two-lane ramp traffic doesn't need to merge at the end of the ramp downstream.
• Safety features like guide rail transitions, crash attenuators, and post-support bases are not designed to offer sufficient protection at risky locations from the opposite direction of travel.

4. Radial or Star and Grid Pattern

In urban planning, roads can be planned from a central point and form grid pattern roads within the radial road lines as shown in Figure 5. This design helps to use grid streets to access blocks and the radial roads act as arterial roads.

Fig.5. Radial or Star and Grid Pattern

Hence this design is the most enduring element of any layout as most streets possess changes in direction and non-systematic street patterns which in turn require systematic planning. 

Advantages

• Helps to keep vehicular traffic safe with a high proportion of 3-way intersections.
• Helps to reduce the cut-through traffic by similar or other means.
• Traffic flow in both directions is improved
• Improve the land use efficiency and unit density

Disadvantages

• The grid pattern increases travel distances for destinations at the corners of the grid and congestion in high-traffic areas. 
• Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they should reduce their travel speed.
• Islands separating the approach and exit lanes, known as splitter islands, should extend far enough.

5. Radial or Star and Circular Pattern

In this road pattern, the main radial roads radiating from the central business area are connected together with concentric roads as shown in Figure 6. Hence, the built-up area planned within the radial roads is formed within the curved block system. 

Fig.6. Radial or Star and Circular Pattern

Advantages

• At regular intersections with stop signs or traffic lights, common crashes include right-angle, left-turn, and head-on collisions. These can be severe because vehicles may be moving through the intersection quickly. With roundabouts, these serious crashes are mostly avoided because vehicles travel in the same direction.
• Using roundabouts instead of traffic signals can also lower the chances of rear-end crashes.
• Roundabouts eliminate the need for drivers to speed up when approaching green lights and reduce sudden stops at red lights.
• Because roundabouts make traffic flow more smoothly, they also cut down on vehicle emissions and fuel usage.

Disadvantages

• The center lines of roads leading to a circular pattern should align properly with the central island.
• The roads approaching the circular pattern should have sufficient curvature well before the roundabout to lower the speeds of entering vehicles.
• Islands between the approach and exit lanes, called splitter islands, should extend enough to offer pedestrian refuge and clearly define the roundabout.
• Ensure that there are adequate traffic signs, pavement markings, and lighting to alert drivers that they are approaching a roundabout and should reduce their speed.
• Older drivers may experience declines in vision, hearing, cognitive functions, and physical abilities, which can affect their driving. Intersections, in particular, can pose challenges for older drivers.

6. Hexagonal Pattern

In this system, the entire area of planning is divided into hexagonal zones. At each of the hexagons, three roads meet. The built-up area bounded by the sides of the hexagons is further divided into suitable zones. 

Each zone has a separate marketing zone and central services surrounded by a hexagonal pattern of roads. Each hexagonal segment is independent in almost all respects.

Advantages

• The hexagons accommodate the convergence of three roads at the boundary of the developed area.

Disadvantages

• It is essential to ensure that traffic signs, pavement markings, and lighting are sufficient to make drivers aware of the need to decrease their travel speed.

7. Linear Pattern

In this particular layout, the roads extend in a linear fashion, possibly influenced by natural elements like the sea or ocean situated on one side of the city.

NOTE: When planning a city anew, specific patterns can be implemented. However, in many cities, existing patterns are already in place and must be adhered to.