Understanding Vehicle Running Speed and Journey Speed

In traffic engineering, vehicle speed can be measured in different ways depending on the purpose. Two important measures are running speed and journey speed.

• Journey Speed: This is the average speed calculated over the entire length of a journey, including all delays and stops. It is calculated as the total distance traveled divided by the total journey time.
• Running Speed: This is the average speed calculated only when the vehicle is actually in motion. It is calculated as the total distance traveled divided by the total running time (total journey time minus any stopped time).

We are looking for a method that allows us to measure both of these speeds.

Measuring Speed: Analyzing the Options

Let's examine the methods provided in the options:

1. Radar speed meters: These devices measure the instantaneous or "spot" speed of a vehicle at a specific location using Doppler radar principles. They are useful for speed limit enforcement or studies at a single point, but they do not measure average speed over a route, let alone distinguish between running and journey speed.
2. Pressure contact tubes: These are pneumatic tubes laid across the road that detect vehicles passing over them. They are primarily used for counting traffic volume and measuring vehicle headway. While they can sometimes be used to estimate spot speed over a short distance, they are not designed for measuring average speed over a long journey or for separating running time from stop time.
3. Moving car observer method: In this method, a test vehicle travels along the road section being studied, typically driven by an observer who records the time taken to traverse the section (journey time) and also notes down any time spent stopped (delay time). The total distance of the section is known. From this data, the journey speed can be calculated using total journey time, and the running speed can be calculated using total running time (journey time minus delay time). This method is specifically designed for obtaining average speeds over a route and can capture both journey and running speed.
4. Enoscope method: This method is used to measure the spot speed of a vehicle. It involves an observer timing a vehicle as it passes between two points a known distance apart using a device like an enoscope (a mirror device). Like radar meters and pressure tubes, it measures speed at a point or over a very short distance, not average speed over a journey.

Conclusion: The Moving Car Observer Method

Based on the analysis, the Moving car observer method is the only method among the options that is specifically adopted for measuring both the running speed and the journey speed of a vehicle over a defined road section or route. It allows for the collection of data necessary to calculate both metrics by distinguishing between total travel time and time spent in motion.