Not enough space, not enough time: the life of a traffic engineer
27 November 2014
Author: Hugh McCarthy BEng MIEI, design engineer, Transport for London
The world population stands at just over seven billion people, up from 5.3 billion in 1990 and anticipated to grow at a rate of 1.2% per year. Considering that at least 54% of these are located in urban cities, with more expected to migrate from rural areas, there is increasing pressure on cities to accommodate growth and maintain services.
One group that has to deal with this particular issue are traffic and transport engineers. Our basic task is to maintain road capacity while ensuring the safety of all its users. Sometimes this is not so basic. In urban areas, there is limited roadspace but an ever-growing influx of commuters. How to use this space in the best way is a matter of much debate.
Shall all our lanes be general traffic lanes? Or we could dedicate one for a bus lane and hope more people use buses? Perhaps we should put in a segregated cycle lane to encourage more cycling? Will this reduce congestion? Will putting in more cycle lanes increase or decrease our road collision rate? Ultimately, trying to solve this problem is like solving a Rubik’s cube with one or two squares missing. We have a lot of users, but not enough space to squeeze everyone in.
So, what to prioritise? In my experience, there has been a move to promote sustainable incentives to do this. Firstly, there is the environmental incentive in that reduction of general traffic can reduce noise and increase air quality.
|POLLUTANT||EMISSIONS thousand tonnes||MAIN SOURCE|
|PM10||178||Construction, mining, quarrying / road transport|
|VOCs||1514||Solvent use / road transport|
Table 1: Sources of common air pollutants in the UK
There is also a health benefit in that using buses and cycling will encourage people to walk more. Commuting by bus will involve some level of walking to and from bus stops – so, over a working week, this adds up. There is also the assumption that buses typically hold 50 passengers so, in theory, this removes 50 cars from the road and increases road space for other users. More importantly, modern cities are always looking to improve their image so a vision of people cycling, walking and having easy access to public transport looks better to tourists than a slow commute of drivers.
But, what if reducing general traffic from two lanes down to one on a particular route will increase or even double existing queuing and lead to blocking the surrounding junctions and roundabouts? This would make our new bus lanes not so reliable to use if buses cannot move forward on the next green light. Subsequently, what if only 10 people are in each bus and the other 40 people have opted to use their cars instead?
This brings us the next solution in that we have to look at entire routes and access the best solution for all, rather than a point-by-point basis. Thus, we need a way to evaluate if our proposals are successful or not.
Traffic for London and modelling
Traffic modelling is a key attribute in this. A variety of packages out there such as LINSIG and VISSIM can estimate the impact of proposals on junctions or entire road networks of a city. If you want to remove a lane at a junction, LINSIG can tell you pretty quickly if this will increase queuing significantly and your road network is over 100% capacity. Furthermore, if a city is planning a strategic route for buses, VISSIM can generate journey times, queue lengths and traffic flow profiles on the surrounding area.
In my work at Transport for London (TfL), we now measure the effort of proposals on our network using Journey Time Reliability (JTR). This is based on the understanding that commuters prefer their journeys to be consistent rather than vary wildly. For example, would you prefer your journey to work be 41 minutes every morning or vary between 30 minutes and 60 minutes? If you left your home at 8:10 each morning, it would be important that you can reliably reach work on time every day rather than on Tuesday and Friday only. Typically, TfLs roads have a JTR of 88% with targets to exceed 90% over the next few years.
All models are wrong, but some are useful.’ But should modelling results have the final say in all of these infrastructure decisions? What if modelling shows that a new pedestrian crossing at a junction will reduce your road capacity by 10%? Should this proposal be discounted because of this one modelling result? What if these crossings were opposite a major rail station and used by tourists, or acted as a link between a popular park and local school/college? Is it worth taking the hit on capacity? Bear in mind that people can walk around live traffic more easily than across it. Maybe this will allow greater accessibility to bus stops? Maybe more people will start using more buses again?
This is where engineering judgment comes in and you make a decision on whether safer pedestrians or more reliable journeys take priority. Ultimately, models are a very useful tool to help you in engineering but will never be 100% accurate. They serve to inform rather than make your decision for you.
E3 – engineering, education and enforcement
One of the more satisfying aspects of the role of traffic engineers is their influence in reducing road collisions and its resultant injuries. Given that our designs affect road speed, vehicle behaviour, suitable carriageway skid resistance and lighting levels, the ability to reduce collision patterns from simple designs is surprisingly effective.
In my student role at the National Roads Authority in the summers of 2005 and 2007, I worked with five years of collision data evaluating the Low Cost Remedial Measures (LCRM) Programme. This programme identified collision trends at different locations around the country and low-cost remedial measures were put in place. As the cost of a road-related death is over €1 million, the simple provision of improved lining and signage can be highly cost effective.
After interventions like these, Ireland has become the sixth-safest country in the EU in terms of road fatalities per 100,000 population. That makes us like Arsenal in terms of the current Premier League table (as of 14 November) but, like Arsenal, we are doing pretty well but can improve.
Much of the above improvement can be attributed to a steady role of education, enforcement and engineering. In the early 1970s, drink driving was accepted, seat-belt-wearing rates were too low, vehicles were yet to be fitted with modern safety equipment such as airbags and a lack of design standards and clear road hierarchy led to speeding on inappropriate roads. Since the turn of this century, there is a heightened awareness of road safety and this work has been reflected in the continuous improvement in the road safety statistics.
It’s the economy, stupid! (the transport economy?)
Overall, governments play a significant role in the outcomes of many transport projects. Simple funding programmes like the LCRM to the continuous enhancement of the motorway and urban road network has made Ireland into a robust nation capable of facilitating new investment and population growth. In London, there are many exciting projects like the Cycle Superhighway Programme, which aims to make London at the forefront of urban cycle infrastructure provision.
Over the next two years, TfL is investing further in order to reduce bus ‘pinch points’ around the city and further reduce bus journey times. This will also be affected by effective pricing that may or may not take commuters back to their cars. It is the role of transport engineers to inform government of the best action on this.
Much of this work has been made possible by transport engineers and improved the quality of life of millions. Roads are no longer the domain of just car users, but have been made accessible to all. The increase of commuters requires us to be ever more creative with solutions that also safe and reliable. A new concept of shared space has merged roads with footways to form a homogenous street where all users can freely move about and traffic speeds are kept below 20mph. It is an example of traffic engineers being innovative with designs and meeting the demands of modern roads. Ultimately, these problems will never be 100% solved but we are always getting closer – and that is why I love it.
Hugh McCarthy BEng MIEI qualified in 2008 with a structures degree at the height of the boom and did traffic modelling for proposed housing projects in Ballymun and Adamstown along with other basic highway design around Dublin and Cork. He moved to the UK in 2011 and worked with AECOM as a transport engineer on London and outer London schemes. McCarthy then joined Transport for London and works on various design projects throughout the city. The goal is to maintain capacity on roads while maintaining comfortable use for all users such as cyclists, pedestrians and other motorists. Contact: HughMcCarthy@tfl.gov.uk