1 Introduction

Since the beginning of 2016, cars were used for six terrorist attacks in countries of the European Union (EU).

Terrorist attacks with use of cars were made in France, Germany, United Kingdom, and Sweden (Rubin and Blaise 2016; Westminster attack 2017; Lkw-Fahrer 2017; Crouch 2017).

Terrorists used the following cars:

  • Off-road vehicle (1 attack).

  • Truck (3 attacks).

  • Van (2 attacks)

Statistics on the terrorist attacks of pedestrian zones made with use of off-road vehicles and trucks have been systematized by the authors in Table 1.

Table 1 The terrorist attacks of pedestrian zones made with the use of off-road vehicles and trucks

The statistics (Table 1) shows that in EU countries there is a problem of protection of pedestrian zones against the terrorist attacks made by means of cars.

Despite high danger of terrorist attacks with use of cars, the majority of pedestrian zones in the cities of EU countries and the cities of other countries of the world have no means of protection from entrance of cars or have insufficiently effective remedies.

As a rule, the following means of protection are applied:

  1. 1.

    antiparking metal columns;

  2. 2.

    bollards.

The first means (antiparking metal columns) cannot be considered as protection against terrorist attacks with use of cars as they are not only capable to stop the trucks but also the passenger cars (Kinney 2013).

The second means (bollards) is usually intended for protection against cars moving at a speed up to 70 km/h and weighing 7  tons (Dawson and Tennant 2008; Krishna-Prasad 2006; Kinney et al. 2014; O’Hare 2012). Such technical characteristics would not allow to stop the truck weighing 20 tons. Without bollard, it is possible to call that these devices have the keen upper edge that is not admissible for pedestrian zones with high traffic, so it can lead to traumatize pedestrians when falling on bollards (Bollard hydraulic FAAC J275 H600 KIT 2013).

1.1 The Resolution of the Problem of Protection of Pedestrian Zones Against the Terrorist Attacks Made by Means of Cars Including Off-road Vehicles and Trucks

The problem of protecting pedestrian zones can be resolved by an anti-ram protective device (ARPD) which will ensure efficient protection against driving into pedestrian zones of the following vehicles:

  1. 1.

    passenger cars including jeeps (off-road vehicles) with high road clearance;

  2. 2.

    motorbikes;

  3. 3.

    trucks.

The specific features of pedestrian zones must be taken into consideration when developing protective devices. Pedestrian zone characteristics can be divided into three groups:

  1. 1.

    Infrastructural

    • pedestrian paths with high traffic—a protective device should not restrict pedestrian circulation;

    • Minimum free space—a protective device must be space saving.

  2. 2.

    Technological

    • High probability of emergency situations. The probability of emergency situations such as fire, terrorist acts, etc. In such situations, vehicles and special emergency service machines including rescue workers, ambulance, police, and others that participate in dealing with emergency situations and evacuating people need free access to the pedestrian zone. A protective device must not obstruct the access of emergency vehicles that arrive at the pedestrian zone for dealing with emergency situations.

  3. 3.

    Legal

    • The owner of a protective device bears responsibility for damage to third parties caused by this device. Developers of the protective device must take into consideration high incoming and outgoing traffic, i.e., the protective device must be safe for pedestrians.

Having considered these pedestrian zones, specific factors that the authors have formulated are five requirements the developed protective device must meet:

  1. 1.

    The protective device must have the capacity to raise and lower the barrage elementto ensure thoroughfare for:

    • rescue workers, ambulance, police (hereinafter—emergency service vehicles), in case of emergency situations including fires and terrorist acts;

    • transport, delivering cargoes for the operation of the pedestrian zone, including equipment, food, etc.

  2. 2.

    The device must be completely independent of external systems including power supply, hydraulic lines, pneumatic lines, etc. (hereinafter—external systems). This requirement is determined by the fact that emergency situations (fire or terrorist act) may cause:

    • electricity cutoff;

    • destruction of hydraulic or pneumatic lines, i.e., switching off of external systems. Being independent of external systems will allow the lowering of the bollard to give emergency services free access to the pedestrian zone even if all external systems are switched off during the emergency situation.

  3. 3.

    The structure and operating mechanism of the device must be simple—this is essential in case of emergency situations (i.e., terrorist act) when the officials of the pedestrian zone may be killed or injured but the bollard can be easily lowered by emergency service employees who come to deal with the consequences.

  4. 4.

    The device must be compact—this requirement is determined by minimal free space on pedestrian zones.

  5. 5.

    The device must be safe for pedestrians—this requirement is determined by the large scale of incoming and outgoing passenger flow on pedestrian zones.

2 Anti-ram protective device design

This anti-ram protective device was designed and patented (patent No RU162412) (Shvetsov 2016) to resolve the problem of protection of pedestrian zones against the terrorist attacks made by means of cars, off-road vehicles, and trucks.

While designing the anti-ram protective device, the author took into consideration the specific features of the pedestrian zones. The ARPD blocks the vehicles by a retractable pillar. The ARPD is located in places of possible penetration of vehicles into pedestrian zones. A general view of the anti-ram protective device is shown in Fig. 1.

Fig. 1
figure 1

ARPD b barrage pillar in lowered position, a in raised position

ARPD has the function of raising and lowering the barrage pillar (Fig. 1). ARPD consists of the following elements:

  • The casing 1, mounted on a concrete foundation 2 (the concrete foundation is leveled with the asphaltic concrete pavement);

  • a blocking element consisting of a cylindrical foundation 4, with a screw hole 5 in the central part and barrage pillar 6 with a mounting hole 7 in its upper part, and a screw element 8 in its lower part;

  • a rubber tightening ring 9;

  • an additional blocking element 10;

  • and a connection element 11.

ARPD meets the five requirements formulated above taking into account the specific features of the pedestrian zones:

  • Requirement 1 ARPD has the function of lowering and raisingthe barrage pillar.

  • Requirement 2 ARPD has a mechanical activator for moving the barrage pillar which is independent of any external systems. The barrage pillar is lowered by twisting into the steel base. The twist insertion is performed through the physical effort of a human being revolving it clockwise with the additional protective element (10 in Fig. 1) which serves as a lever. The barrage pillar has a screw element in its lower part; this element fits into the hole in the case of the foundation. This hole has a thread for twisting the screw element to lower the barrage pillar; when rotated in reverse (unscrewed), barrage pillar raises.

  • Requirement 3 structure of ARPD is maximally simplified and allows anyone without special training to lower the barrage pillar in 1–1.5 min, which ensures emergency service vehicles thoroughfare when they arrive.

  • Requirement 4 ARPD the diameter of the barrage pillar is only 350 mm which is sufficiently compact.

  • Requirement 5 ARPD has the special shape of a barrage pillar rounded in its upper part and has no sharp corners or projecting parts.

ARPD meets all the requirements formulated taking into account the specific features of pedestrian zones and, therefore, it can be applied to protect pedestrian zones against the terrorist attacks made by means of cars (including off-road vehicles and trucks).

3 Types of the Vehicles the ARPD is Aimed at

3.1 Protection Against Jeeps (Off-road Vehicles) with High Road Clearance

To make ARPD capable of protecting against vehicles with high road clearance, we need to know the maximum road clearance of such vehicles. We have collected data on vehicles with the maximum road clearance (Table 2).

Table 2 Vehicles with maximum road clearance (series produced)

According to the data obtained, the maximum clearance of the vehicles under study is 460 mm. The height of the barrage pillar above the road surface is 800 mm which ensures blocking motor cars (jeeps) with maximum clearance.

3.2 Protection Against Motorbikes

The developed ARPD can block both cars and motorbikes.

An additional blocking element performs this function in ARB (this element is depicted as component 10 in Fig. 1). The additional blocking element is a steel pipe with the following specifications:

  • length 1300 mm;

  • diameter 40 mm;

  • wall thickness 5 mm;

  • is made of high-strength steel of the 5XHM (RUS) type (US analogue—L6 (AISI/ASTM); Germany (DIN/BOHLER)—1.2713 55NiCrMoV 6).

The blocking element is inserted into the mounting hole of ARPD to form the element that blocks movement of motorbikes. Blocking elements also have holes in the edges. Stopper brackets are inserted into the edges of the adjoining elements (element 11 in Fig. 1). These brackets join additional blocking elements together.

3.3 Protection Against Trucks

We conducted special research to calculate the maximum mass/weight of a potentially intruding vehicle, which the ARPD must be capable of blocking. The calculation is based on the analysis of maximum weight of vehicles that had been used in terrorist attacks.

We have found that the maximum weight of the truck used during the terrorist act committed on August 1st 2003 in Mozdok (Russia) was 19,050 kg (Istoriya terrora na kolesah 2011). In the authors’ opinion, the calculated maximum weight should be increased to 20,000 kg to improve the reliability of protection.

Thus, we have established that one ARPD must block a motor vehicle weighing 20 tons driving at 40 km/h (this design speed was taken as the basis for calculations). Blocking vehicles of larger weight driving at higher speeds is possible at the expense of more dense spacing of ARPD. In this case the vehicle trying to enter will contact not only one but two or more ARPD.

4 Experimental Testing of ARPD

We assume that the only option to check whether one ARPD is capable of stopping a vehicle weighing 20 tons at 40 km/h is experimental. We have conducted a field experiment to test the developed ARPD.

4.1 The Goal of the Experiment

The anti-ram protective device is aimed at forming a physical obstacle to prevent the attempt of a motor vehicle to drive into the pedestrian zone.

The goals of the experiment are as follows: to confirm the capability of the anti-ram protective device to block a vehicle weighing 20 tons and driving at 40 km/h; to obtain results of the shock load impact on the structures of the device under testing.

4.2 Object of the Experiment

An anti-ram protective device installed in the center of the traffic zone of a road.

4.3 Technical Features of ARPD

  • height of the barrage pillar is in a raised position above the road surface, 80 cm;

  • diameter of barrage pillar is 35 cm.

4.4 Specified requirements imposed on ARPD

ARPD must form an insuperable obstacle to a vehicle weighing 20 tons and driving at 40 km/h.

4.5 Experimental Technique

The experiment is performed by ramming the anti-ram protective device with the “KamAZ” vehicle (weight 20 tons, speed 40 km/h).

The truck gathered speed on a horizontal road with hard coating (asphalt concrete) of 6 m wide. The vehicle moved in the assigned direction along a rectilinear monorail.

The vehicle was accelerated by a truck tractor using a snake line, a system of movable and stationary guiding blocks, and a slider that moved along the monorail. Then the vehicle was automatically detached from the slider at a distance of 8 m from the contact point with ARPD. The vehicle’s further movement was due to inertia.

The speed of ram impact of the vehicle on the ARPD was determined by an electronic device “time–distance” at a distance of 8 m from the vehicle–ARPD impact point.

4.6 Experimental Results

The experiment testing the properties of the anti-ram bollard with a “KamAZ” truck was conducted on August 20th 2015.

Actual experiment modes:

Mass/weight of the vehicle, kg

20,100

Impact velocity, km/h

40.7

Angle of contact, °

90°

Air temperature, °C

+21

Wind speed, m/s

3–4

4.7 Operational Characteristics

The “KamAZ’ truck rammed ARPD at a speed of 40.7 km/h. In the center of the shock impact the deformation of the barrage pillar was 137 mm, cracks formed in the area of the ARPD foundation, no other observations were noticed.

After the ram impact, the truck sustained significant damage to the frame and cabin, and moved forward by the distance of 137 mm which equals the deflection value of the barrage pillar.

4.8 Conclusions

The anti-ram protective device meets the assigned requirements, the experiment conducted has shown that an anti-ram protective device can block a truck weighing 20 tons driving at 40 km/h in case of it entering the pedestrian zone.

5 The Location of ARPDs for Protection of Pedestrian Zones

We considered the following variants of locating ARPDs:

  1. 1.

    along the edges of pedestrian zone—at the border between the pedestrian zone and the traffic area;

  2. 2.

    along the edges of the traffic zone—at the border between the pedestrian zone and the traffic area.

When located along the edges of the traffic area, ARPD (even considering its small size) may cause a traffic accident as a result of being hit by passing cars. This variant is, therefore, unacceptable although it is of maximum comfort for pedestrians moving in the pedestrian zone.

A location along the edges of the pedestrian zone can be considered as optimal (Fig. 2).

Fig. 2
figure 2

The layout of the optimal location of ARPDs

To prevent small vehicles from driving between installed ARPD, we need to correctly calculate the spacing between ARPD. First, we need to calculate the maximum distance apart from the arrangement of ARPD.

To calculate the maximum permissible distance between anti-ram protective devices that will ensure guaranteed blocking of the passage of small vehicles, we need to know the minimum dimension parameters of existing cars. For this purpose we have analyzed standard motor vehicles with minimum dimension parameters (Table 3).

Table 3 Standard vehicles with minimal dimension parameters

Following the analysis, we have obtained data on the minimal width of a vehicle which is 1475 mm. To resolve the problem of guaranteed blocking of vehicles, we must introduce the reliability index (constricting the maximum distance between ARPD), which is adopted as 10% of the established minimal width of a vehicle. This is determined by a theoretical probability of driving vehicles into a station that either have not been considered during our research or are non-standard, i.e., those with less width. The maximum distance between the anti-ram protective devices D max is calculated according to the formula:

$$ D_{ \hbox{max} } \; = \;X_{\text{vh}} {-} \, (X_{\text{vh}} \cdot X_{\text{br}} ) \, {-}X_{\text{pp}} , $$
(1)

where X vh is the width of the vehicle, mm; X br is the vehicle blocking reliability index; X pp is the diameter of the barrage pillar, mm [i.e., if X vh = 1475 mm (data from Table 3), X br is 10% of X vh, X pp = 350 mm, so D max = 977.5 mm].

The density of spacing anti-ram bollards D pl is determined by the formula:

$$ D_{\text{pl}} \; = \;D_{ \hbox{max} } \; + \;X_{\text{pp}} . $$
(2)

Thus, if D max = 977.5 mm, X pp = 350 mm, the spacing density of ARPDs calculated according to formula (2) is one device per 1327.5 mm.

6 Conclusions

The authors have developed an anti-ram protective device capable of blocking motor cars including off-road vehicles and trucks, as well as motorbikes. While developing the anti-ram protective device, the authors took into consideration the specific characteristics of pedestrian zone. Equipping pedestrian zone with such devices will resolve the problem of protection of pedestrian zones against the terrorist attacks made by means of cars (including off-road vehicles and trucks), as well as motorbikes. It will preserve lives of people who might be killed as a result of such intrusions into pedestrian zones.