First, you will need to look at all available entry and exit points on your site. Differentiate between the areas with the highest traffic flow per hour and the lowest. The areas with a high traffic flow will need securing with products able to cope with considerable duty cycles such as an automatic rising arm barrier or a bollard system designed to control traffic flow.
Areas with minimal traffic flow may only require securing with telescopic security bollards. Which can be lowered in the morning and then raised again in the evening when the site closes.
Thought needs to be paid to the type of visitor wanting to access the site. Employees arriving in the morning may need to be treated differently to unknown visitors approaching throughout the day.
Depending on the access control objective, there is the physical barrier which needs to be selected; i.e. whether you require high security bollards or rising arm barriers and then the control system. This system is the brains behind the product and has the ability to control barriers as required. Systems can be accessed using an identity card, ANPR or a keypad system. The options are almost endless.