Practitioners and policy makers are increasingly looking to reliable research evidence to inform their decisions. Making sense of the research evidence can be challenging, however. There may be a very large number of studies making claims about the effectiveness of an intervention. These individual studies may vary in their scientific rigour. They may also produce inconsistent and conflicting findings. Traditional literature reviews are one method of summarising the research evidence, but these are often biased and difficult to replicate. Systematic reviews, by contrast, follow a particular method that aims to minimise bias and provide a transparent and comprehensive appraisal of the research evidence.
But systematic reviews are not limited to questions about whether a particular intervention is effective. As we show in our review of alley gating, a systematic review can also usefully provide information on how an intervention works, establish whether an intervention is cost effective and set out some of the likely implementation challenges.
What is alley gating?
Alley gating is a type of situational crime prevention. It refers to the use of lockable gates, usually made of steel or iron, which are designed to restrict entry to an alley. Individuals whose properties border the gated alleys typically receive a key or passcode to operate the gates. The intention is to restrict alley access only to those legitimate users in possession of a key or passcode. Although alley gates are generally installed to reduce burglary, they may also reduce opportunities for other crimes that commonly occur in alley ways such as flytipping, prostitution, dog fouling and drug dealing.
What did the systematic review tell us about the impact of alley gates on reducing crime?
The evidence we reviewed suggests that alley gating is an effective burglary reduction measure. Of the six evaluations that we identified, four reported statistically significant reductions in domestic burglary following the installation of alley gates, relative to a control area. As with most other forms of situational crime prevention, we found little evidence of any displacement to other geographical areas. We found no studies that reliably measured the impact of alley gates on other forms of crime.
How do alley gates reduce crime?
The literature we reviewed suggested several ways in which alley gates may reduce crime. By far the most common mechanism was that alley gates act as a physical barrier which makes it harder for offenders to gain access to the alley. Other mechanisms through which alley gates might reduce crime ranged from residents taking greater responsibility for guarding and monitoring the gated alleys, to alley gates reducing the potential rewards of crime by limiting the sorts of items they can feasibly remove from burgled properties.
Regrettably, information was not available in the primary studies we reviewed to test whether the identified mechanisms were responsible for the outcome patterns observed.
It is important to consider the type of neighbourhood in which alley gates are to be implemented. Affected residents need to be invested in their area. In neighbourhoods with a high turnover of residents (such as students), lots of people will have access to keys or key-codes to operate alley gates, which could undermine their effectiveness. Moreover, if residents are willing to come together and use alley gates effectively and efficiently, they are more likely to see the desired reductions in crime than if there is disagreement about their implementation and usage.
How do you implement them to get the best impact?
It is important to consult both residents and local authorities (such as refuse collection and the emergency services) who may be affected by an alley gating scheme. The former must agree to the rules about how the gates are to be used, and accept responsibility for implementing these rules. The latter must confirm that alley gates in no way compromise service delivery. Moreover, the features of the gates themselves are important. There is much diversity in the design of alley gates, reflecting the different uses and users of urban alleyways. The type of alley gate and locking mechanism must suit the intended users. If keys are to be used, then everyone who requires access to the alley must have a key.
What do they cost?
In monetary terms, we concluded that the reductions in burglary associated with the installation of alley gates generally exceeded the investment required to install and maintain them. Although the cost per gate varied considerably –from £158 to £1,453 depending on the different requirements in different study areas – a conservative estimate is that for every £1 spent on alley gating results in a £2.19 benefit.
You can download the full systematic review and access additional information by visiting the Alley gating page of our What Works: Crime Reduction Systematic Review Series.