FRAME CONSTRUCTION Unibody and Space Frame - This type of construction links frame sections together for greater strength. As car designs have become more aerodynamic the windshields have become swept back. This means that the "A" pillar is not as upright as in older car designs. In a roll over the swept back "A" pillar must still prevent the roof from crushing under the weight of the vehicle. Designers have used a combination of material and form to achieve the required strength. High Strength Low Alloy (HSLA) steel is often used in modern auto frames. This material is inherently stronger than normal steel. In addition manufacturers use HSLA in a corrugated configuration adding more to its strength. In many vehicles today the windshield also provides structural support in roll over type crashes. In the pillars and cross members of the Space Frame design, Urethane foam is being used to make the body stronger and the cabin quieter. These reinforced pillars can be very difficult for some hydraulic tools or reciprocating saws to cut. Monocoque - This is a frame design is where the frame and sheet metal becomes one. This technology provides the strongest steel body for the weight. A variety of steel is being used in the construction of monocoque bodies. HSLA is common in these frames. As noted above, High Strength Low Alloy steel is three times stronger than low carbon steel and is being used in the roof pillars, cross roof members, cross floor beams and other areas of frames to increase crush resistance now mandated by NHTSA and NTSB. This makes cutting and spreading more of a challenge. Micro-Alloy and Boron Steel are also used in the sub frame, doors and cross cowl member. The cross cowl member is located behind the instrument panel and connects the two A-pillars. Severing the cross member prior to pushing the dash forward, relieves the rigidity of the vehicle and thereby will allow you to make more space available for extricating your victim. Cutting Micro-Alloy or Boron Steel presents an extremely difficult challenge for most of the hydraulic cutters currently on the market. See the discussion on Frame Materials for more information on HSLA and Micro-alloy material.