Focus of the intervention
Alley gates are lockable gates installed to prevent access by offenders to alleyways, such as those which run along the rear of older-style terraced housing in the UK. While normally a burglary prevention tool, alley gates can also prevent other crimes such as littering and anti-social behaviour by preventing access to alleys by non-residents and better controlling the space.
Alley gates are usually made of iron or steel, and are bespoke in relation to the requirements and specifications of an individual alley. The residents of homes adjacent to the gated alley are then left to operate the gates, either using keys or a key code.
This narrative is based on one review of 43 studies. The outcome measured was a reduction in police recorded burglaries.
Effect – how effective is it?
Overall, the evidence suggests that alley gating has reduced crime.
When the authors calculated an overall effect size using six studies with higher quality methodological designs, a statistically significant reduction in domestic burglary rates was found in comparison to control areas.
Four of the six individual studies included in a statistical meta-analysis reported statistically significant reductions in burglary, and none reported increases.
It is important to note that the review authors found no evidence of crime being displaced to surrounding areas, but instead a diffusion of benefits was found. That is, burglary rates in the areas surrounding the gated areas showed a decrease, though this decrease was not statistically significant.
How strong is the evidence?
The review was sufficiently systematic that most forms of bias that could influence the study conclusions can be ruled out.
The review considered many elements of validity, conducting relevant statistical analyses and using multiple coders to ensure the accuracy of information collected. It considered the possibility of publication bias, as well as ensuring that only studies of comparable quality were pooled to create an overall effect size. The authors also conducted analyses of possible displacement and diffusion of benefits following the intervention.
Mechanism – how does it work?
The review identified a number of different ways in which alley gates may reduce or increase crime. However, information was not available from the primary studies to test whether these mechanisms were responsible for the outcome patterns observed. Specifically these mechanisms included the following.
- Alley gates are physical barriers designed to prevent access to alleys and connected properties, and are difficult to climb over or crawl under. Therefore they might decrease crime by increasing the effort required for offenders to commit burglary (and other crimes).
- Residents are encouraged to be responsible for closing the gates and controlling access to them which is believed to increase guardianship and surveillance, which in turn might reduce crime.
- Residents are encouraged to see the alley as their territory and take an interest in the behaviour of people who access it – therefore the gates may plausibly increase territoriality.
- Offenders can also no longer use the excuse that they didn’t realise access was prohibited, as gates physically mark the boundaries to where they can and cannot access and are often accompanied by signage.
- Applying the concept of broken windows suggests that open alleys are unregulated spaces where signs of disorder are produced, creating a permissive environment for crime. By gating the alleys and creating orderly and clean spaces, cues are provided suggesting that this is not a suitable place to offend, and that the risk of detection is high.
- Alley gates may also work through deflection. This suggests that gating some alleys may reduce the attractiveness of the area more generally to offenders, and remove it from the awareness space. Since offenders can no longer pass through networks of alleys uninhibited, they may no longer offer an attractive space in which to offend.
- Alley gates may reduce the rewards to offenders by limiting the items which are possible to remove during offences. If an offender can no longer easily access, and escape from alleys, they are no longer able to remove large items or those not easily concealed and carried.
- One way in which alley gates may act to increase crime is by reducing guardianship – if gating the alleys reduces their usage by legitimate individuals such as residents, then guardianship and natural surveillance may decrease. This could then increase perceptions of anonymity of potential offenders.
Moderators – in which contexts does it work best?
Within the review, a variety of contextual factors, which could impact upon the effectiveness of alley gates were discussed, as listed below. The absence of data in the primary studies meant that these could not be tested.
- Alley gates are not suitable for all types of crime, and are specifically designed for those crimes that occur in, or are facilitated by access to alleyways. If burglars enter homes through the front of properties, for example, then gating access to the rear of these properties may not reduce burglary.
- The neighbourhood in which alley gates are implemented may have an impact upon their effectiveness – those communities with a high turnover of residents may mean that many people have access to keys or key codes without necessarily having any investment in the area.
- There is a need for resident and community investment in the alley-gating scheme. 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.
- Finally, the physical environment is important – alley gates must not create an environment that appears to be uncared for, such as preventing refuse collection. Gates must be carefully designed and appropriate to the context in which they are to be installed or they may be inappropriate for crime reduction purposes.
The review authors suggest a number of combinations of contexts and mechanisms which may be favourable (or not) to reducing crime:
- While gates may decrease crime if criminals are coming to the gated street from elsewhere, they may not work if the criminals are resident within the gated area.
- The types of residents in the areas where gates are introduced may reduce the efficacy of the gates – in areas with low residential turnover where neighbours know each other gates are more likely to be used effectively. However, where there is a more transient population, where there is mistrust amongst neighbours or a lack of consensus about the use of the gates, they may not be used diligently and/or correctly, which may affect the crime rate.
- The attributes of the alley itself may also influence the efficacy of the gates. For those alleys that are open to surveillance by residents and where residents clearly own the space, then it may be easier to maintain control over the area. Where they are not visible to residents, or ownership is unclear, then gates may not encourage an increase in natural surveillance and guardianship.
- Local service providers need access to alleyways to maintain them (e.g. to collect rubbish) and to provide emergency services if the alleyways are to be seen as cared for and crime free.
- Finally, the attributes of the gates themselves must be favourable to crime reduction – they must be tall enough and robust enough to repel offenders, as well as self-locking. If they are flimsy, easily scalable or often or easily left open then they may not reduce crime.
Implementation – what can be said about implementing this initiative?
The review noted a number of important factors which must be considered to successfully implement alley gates.
There must be full consultation with residents leading to their consent to the scheme. The proportion of residents who need to agree to gates being installed may vary depending on the area. This ties into the importance of resident commitment to the implementation and usage of the gates. Residents must agree to the rules about how the gates are to be used, and accept responsibility for implementing these rules.
The importance of early consultation with local authorities is highlighted by the review, so that local services such as refuse collection and the emergency services are not compromised by the implementation of the alley gates.
The status of the alley is also relevant – who owns the alley may affect the installation of the gates. If the alley is a public right of way it is potentially more complicated to get permission to install the gates. If the alleys are owned by the home-owners, it may also require all owners to agree, which may be complicated in areas with high levels of rented properties. Finally the features of the gates themselves are important – the gates and the locking mechanisms must suit the users. If keys are to be used, then everyone who requires access to the alley must have a key.
Economic considerations – how much might it cost?
The review synthesised information about the costs of alley gates from the primary studies where provided, and conducted a cost-benefit analysis of the five studies which provided enough information to do so. The cost per gate for the alley gates ranged from £158 to £1453.21 across six studies, with an average cost per gate of £728.
The costs of the gates varied significantly due to the different requirements for the gates in different areas. Only one of the studies showed a negative cost-benefit ratio, and conservative estimates of the benefit to cost ratios ranged from minus £2.79 for each £1 spent, to £2.19 benefit per £1 spent. Where appropriate, the primary studies included not only the costs of the alley gates, but also those for other interventions implemented.
Overall, the evidence suggests that alley gating has reduced crime. A diffusion of benefits to surrounding areas has also been detected.
Alley gates work by reducing the access of potential offenders to the rear of houses, and while commonly a burglary reduction initiative, can also reduce other crimes that occur in alleys such as anti-social behaviour and littering. The residents of the alleys to be gated should be consulted and be willing to use the gates correctly in order for them to be effective. The gates were found to generally be cost effective, although the cost of the gates varied widely depending upon location and requirements.
Sidebottom, A., Tompson, L., Thornton, A., Bullock, K., Tilley, N., Bowers, K. and Johnson, S. D. (2015) Gating Alleys to Reduce Crime: A Meta-Analysis and Realist Synthesis
This review is number 1 in the Systematic Review Series. These were commissioned as part of a consortium of universities in the Commissioned Partnership Programme.
Summary prepared by
This narrative was prepared by UCL Jill Dando Institute and was co-funded by the College of Policing and the Economic and Social Research Council (ESRC). ESRC grant title: 'University Consortium for Evidence-Based Crime Reduction'. Grant reference: ES/L007223/1.