Why your startup’s Truck Number might be lower than you think

In software engineering, the Truck Number (also known as the Bus Factor) measures how many key people can leave before a project is in serious trouble. A Truck Number of 1 means a single person holds critical knowledge - if they disappear, everything grinds to a halt. In startups, where teams are small and highly specialized, this risk is even greater. Founders, lead engineers, and early employees often accumulate institutional knowledge that isn’t written down, making them single points of failure.

Startups, by their nature, push for speed over redundancy. A lean team is efficient but fragile. If only one developer understands the core architecture, or a single data scientist fine-tunes the AI model, losing them could be catastrophic. Documentation and cross-training take time, and when shipping features is the priority, those practices are often overlooked. But when the inevitable happens - whether through burnout, new job offers, or personal emergencies—the team scrambles to recover lost expertise.

AI has added a new dimension to the Truck Number problem. Many machine learning models are developed by a handful of experts who understand not just the code but the reasoning behind the training data, hyperparameters, and trade-offs. Unlike traditional software, AI models are often difficult to interpret, making it even harder for a new engineer to step in. A startup’s AI pipeline might rely on a single person who built it, meaning the Truck Number is effectively 1. Worse, if the model is undocumented or trained on proprietary data, even a new hire may struggle to replicate previous work.

Ironically, AI itself might help mitigate this issue. Code-generation tools like GitHub Copilot and AI-assisted documentation tools can reduce dependency on any one individual by making code more accessible. Startups can also use AI to automate repetitive tasks, freeing up senior engineers to focus on knowledge-sharing. However, these tools are no replacement for a strong engineering culture that values redundancy, shared ownership, and clear documentation.

Ultimately, a high Truck Number should be a deliberate goal, not a happy accident. Regular knowledge-sharing sessions, better documentation practices, and pairing junior developers with experienced team members all contribute to long-term sustainability. In startups and AI-driven teams, where innovation moves fast and talent is scarce, the ability to continue without any single person is a competitive advantage. If your Truck Number is too low, it's not just a risk - it’s a ticking time bomb.

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